Martha Jones, the Doctor's new companion who at this stage is yet to meet him, walks down the street juggling phone calls from her family. The calls relate to her brother's upcoming 21st and whether their father should be there with his new girlfriend.
The Doctor walks up to her and makes a point of taking his tie off in front of her, before walking away. Martha of course has no idea what just happened, but doesn't do anything more.
She arrives at a hospital, and as she enters, she is pushed aside by someone dressed in black and wearing a black helmet. Think the original Stig from Top Gear and you'll know what the person looks like.
Martha stands in front of a locker, putting on a white coat, which suggests that she works at the hospital. She touches the locker door, and a visible electric spark shocks her.
We then discover that Martha is a student doctor, as she is gathered around the bed of a patient together with other students and Mr Stoker, the head doctor, asks some of the students, including Martha, what they think is wrong with the patient, and they give unsatisfactory answers. He asks the patient what she had eaten recently, and determines that she is suffering from a salt deficiency.
Mr Stoker takes the students to another ward, and they walk past the man in black who Martha encountered earlier. He is joined by someone dressed identically, and the two of them walk off without saying a word.
They arrive at the next patient, who is the Doctor, going by the name of John Smith. Mr Stoker asks Martha to examine him, and she comments on having met the Doctor earlier that morning. The Doctor appears to have no idea what she's talking about, and says that the nurses can confirm that he's been in the hospital since the previous evening.
Martha listens to the Doctor and discovers his two hearts, but says nothing after the Doctor winks at her. Mr Stoker criticises Martha's technique, and picks up the Doctor's chart, receiving a shock in the process. Martha remarks that she got was shocked earlier, and other students relate similar accounts.
Later on, Martha is on the phone to her sister, Tish. Martha comments that it's raining outside, but Tish, who is near the hospital, says that it's not raining where she is. Tish walks around a corner and sees the hospital, which has a cloud over it, and is the only building being rained on.
As Martha is talking, she notices the Doctor walk past, but she ignores him. A fellow student points out to Martha that the rain is going up, a moment before Tish tells her the same thing. There is a flash of light, the building shakes, and when it stops, the hospital's occupants discover that the building is now on the moon.
Back in London, there is a large hole where the hospital used to be. While Tish tries to contact Martha on her phone, we can see the TARDIS in the background.
Back on the Moon, Martha tries to calm down the patients. She walks over to the window and reaches to open it, but is stopped by the other student, who says that all the air will be let out.
Martha points out that the windows aren't air-tight, so if the air was going to have been sucked out, it would have already happened. The Doctor appears at this moment, and commends Martha for raising a good point. He asks Martha if there's a balcony on the floor they're currently on, and when she tells him that there is, he invites her to join him outside.
The two of them step out on to the balcony, and discover that there's still air. Martha comments on the beauty of the moon, and also remarks that it's her brother's birthday party that evening.
Martha asks the Doctor what happened, and he turns it around by asking her what she thinks happened. Martha says that it has to be aliens, and lists some of the events that we've seen in previous seasons.
She goes on to say that she had a cousin, Adeola, who worked at Canary Wharf when the Cybermen appeared. Adeloa was also played by Freema Agyeman, so that's a neat way of explaining the uncanny resemblance, even if cousins with that degree of similarity don't exist in real life.
The Doctor says that he was at Canary Wharf, and he introduces himself as “The Doctor”. Martha, being a trainee doctor, is a little sceptical about his title, and refuses to call him by it, saying that he has to earn it.
Three large spaceships fly overhead and land near the hospital. Spacesuited aliens exit the ships and begin marching towards the hospital, and the Doctor identifies them as Judoon.
Florence Finnegan, the female patient from earlier, enters Mr Stoker's office and says that she needs his help. Mr Stoker says that he doesn't think that he can help, but Florence says that he can. The two people in black enter the office and hold him down while Florence proceeds to drink his blood through a straw, although we don't actually get to see that sequence.
The Judoon enter the hospital and the leader takes his helmet off, to reveal a rhino-like head. After one of the doctors tries to speak to the Judoon, the leader uses a device which is able to assimilate the language and allow it to speak in English. The Judoon leader announces that all suspects will be catalogued, and the Judoon begin to scan the patients and staff with a device, marking their hands if they're human.
The Doctor and Martha watch this happen while hidden behind some plants. The Doctor explains that the Judoon are interplanetary police for hire, who have brought the hospital to the moon as they have no jurisdiction over the Earth and the moon is neutral territory. The Doctor says that if they're looking for non-humans then it's bad news for him, to which Martha expresses her disbelief about his being an alien.
The Doctor and Martha head away from the Judoon at a run, which is only the first of many times Martha will run with the Doctor. Meanwhile, the Judoon finish the ground floor and move on to the higher floors. One of the patients tries to attack a Judoon, who disintegrates him with a ray gun.
The Doctor finds a computer and tries to look through the hospital records. While he's searching, he tells Martha that he wasn't really looking for trouble, but as he was walking past the hospital he noticed the plasma coils and so checked himself in.
The Doctor discovers that the Judoon have wiped the hospital records, and Martha decides to go and ask Mr Stoker if he's aware of any patients with unusual symptoms. Martha enters Mr Stoker's office, where she discovers Florence busy drinking his blood. Florence orders the men in black to go after Martha.
Martha meets up with the Doctor, and the two of them start running again. They reach the X-ray department, and enter a room with an X-ray machine.
The Doctor tells Martha to press the button on his signal. She doesn't know which button it is, but luckily for her there's an operator's manual nearby, and while the Doctor sonics the machine, Martha scans through the manual.
The man in black enters the room, and the Doctor tells Martha to press the button. She presses a button which looks like it was pretty obviously the button she would have had to push, and man in black falls down, dead. The Doctor explains that he increased the radiation by 5000 percent, but that sort of radiation can't harm him.
He tells Martha that the man in black was a creature known as a Slab, which is a basic slave drone. While Martha tries to tell him about Florence, the Doctor notices his sonic screwdriver, which has been burnt out my the radiation, and starts lamenting its loss. Martha attracts his attention by calling him “Doctor”, and the Doctor is quite pleased about that.
When Martha tells the Doctor about Florence drinking Mr Stoker's blood, he realises that Florence is an internal shapeshifter. If she assimilates human blood then she'll appear human to the Judoon scanners. This point is demonstrated by a scene of the Judoon scanning Florence and marking her as human.
The Doctor and Martha hide from the second Slab, but are then confronted by a group of Judoon who scan the Doctor and establish that he's not human. This finally convinces Martha that the Doctor is an alien, but she doesn't have time to dwell on it as they have to run again.
The Doctor and Martha escape from the Judoon, but notice that the air is running out and patients are gasping for air. The Doctor tries to imagine what Florence will do next and spots an MRI sign and realises something, but any explanation is cut off by the arrival of more Judoon.
The Doctor says that he needs Martha to hold the Judoon up. He says that she must forgive him and then kisses her before heading off the MRI. So in the new series the Doctor has now kissed both his long-term companions in a non-romantic context.
The Doctor arrives at the MRI and finds Florence doing something with the equipment. He pretends to be a patient freaked out by the Judoon, and Florence orders the remaining Slab to hold the Doctor.
The Judoon approach Martha and scan her. The scan reveals that she is human, but there are non-human elements as well, and the Judoon leader orders a full scan.
In the MRI room, the almost obligatory villain “reveals plan to hero” scene is taking place. Florence tells the Doctor that she's altered the MRI machine to send out magnetic pulse that will kill every living thing with 250,000 miles, with the exception of her, as she's be safe in the room. Once everyone is dead, the Judoon ships will be hers so that she can make her escape.
Florence reveals that she's an alien, but also points out that she's been scanned and been found to be human. The Doctor tells her that he overheard one of the Judoon leader ordering the other Judoon to increase their scan to Setting Two, as a result of not being able to find the non-human.
Florence says that she will need to assimilate more blood, and pulls her straw out of her bag. She place it up against the Doctor's neck and begins to drink his blood.
After the Judoon have given Martha a full scan, the leader gives her a pamphlet, which he states is compensation. The Judoon and Martha then head to the MRI where they discover the Doctor's body lying on the ground.
The Judoon leader scans the Doctor and states that he's dead and the case is closed, although anybody watching knows that the Doctor isn't actually dead as there's another episode next week.
Martha accuses Florence of being non-human, but she holds up the mark that the Judoon made and says that she's human. Martha realises that if Florence assimilated the Doctor's blood then she'll register as non-human on the scanners.
Martha grabs a scanner from one of the Judoon and uses it to scan Florence. The scanner registers non-human, and the Judoon leader states that Florence is sentenced to death. The Judoon kill Florence and the remaining Slab, but not before Florence is able to activate the MRI.
The Judoon leader scans the MRI machine and announces that a lethal build-up has been detected. He orders the Judoon to evacuate, despite Martha's protests, saying that their jusridiction has ended.
With the air running out, Martha tries to resuscitate the Doctor. She performs standard CPR before remembering that he has two hearts, and begins compressions on both sides of the Doctor's body. The Doctor recovers, and Martha is able to advise him about the MRI before she collapses as a result of the lack of air.
The Doctor reaches for his sonic screwdriver, which is no longer there. However, he is still able to deactivate the machine by using the highly sophisticated technique of unplugging it.
The Judoon ships take off, and it begins raining on the hospital again. There's a flash of light, and the hospital returns to London.
In the aftermath of the hospital's return, Martha catches sight of the Doctor walking to the TARDIS while Tish is talking to her. Martha turns to look at Tish and when she turns back, the TARDIS is gone.
Later on, Martha is listening to the radio while preparing for the party. A comment is made that Mr Saxon has been proved right, and humans are not alone in the universe.
At the party, Martha's mother, Francine and the new girlfirend, Annalise get into an argument and Annalise storms out, while the rest of Martha's immediate family is gathered at the door. Everyone goes in different directions, and Martha notices the Doctor standing at a nearby corner.
She follows him around the corner, and discovers the TARDIS. In the background is a poster saying “Vote Saxon”.
The Doctor invites Martha to go on a trip with me. She turns down the invitation, saying that she has too many things to do.
The Doctor tells her that the TARDIS can also travel through time, which she doesn't believe. The Doctor says that he'll prove it to her, and enters the TARDIS.
The TARDIS disappears and then reappears, and the Doctor emerges again, holding his tie in one hand. Martha comments on the lack of room inside the TARDIS, and the Doctor invites her to take a look inside, with the usual amazement at discovering something bigger on the inside.
As the Doctor takes his place at the controls, Martha asks if there's any crew. The Doctor tells her that there isn't, although he did have a friend called Rose, who is now with her family.
He tells Martha that she's not replacing Rose, and this is just one trip to say thank you. There's some flirty comments from Martha, and then the TARDIS takes off, with the Doctor welcoming her on board. The final shot is that of the TARDIS travelling through a blue vortex, indicating that they're heading back in time.
Quotes
Mr Stoker: That's only to be expected. There's a thunderstorm moving in and lightning is a form of static electricity, as was first proven by - anyone?
The Doctor: Benjamin Franklin.
Mr Stoker: Correct!
The Doctor: My mate Ben, that was a day and a half. I got rope burns off that kite, and then I got soaked..
Mr Stoker: Quite...
The Doctor: ... and then I got electrocuted.
Mr Stoker: Moving on.
(aside)
I think perhaps a visit from psychiatric.
The Doctor: Oh, look down there, you've got a little shop. I like a little shop.
Martha: What's that thing?
The Doctor: Sonic screwdriver.
Martha: Well, if you're not going to answer me properly!
The Doctor: No, really, it is. It's a screwdriver, and it's sonic. Look.
Martha: What else have you got? A laser spanner?
The Doctor: I did, but it was stolen by Emily Pankhurst, cheeky woman.
Martha: You're completely mad.
The Doctor: You're right. I look daft with one shoe.
The Doctor: How are you feeling? Are you all right?
Martha: I'm running on adrenaline.
The Doctor: Welcome to my world.
Martha: What sort of species? It's not every day I get to ask that.
The Doctor: I'm a Time Lord.
Martha: Right! Not pompous at all, then.
The Doctor: Crossing into established events is strictly forbidden. Except for cheap tricks.