In an English Boarding school Smith, a teacher, walks the corridors and teaches his lessons, whilst Martha and her companion Jenny go about their cleaning work, heckled by the senior boys of the school.
Some time later Smith carries a large pile of books around the school, encountering the school matron on the way. She helps him with the load and together they make their way around the school, Matron (alias Nurse Joan Redfern) taking the opportunity to ask him if he will be attending the annual local dance. He begins to splutter a reply but manages to fall down the stairs before he can give an eloquent response.
Soon Joan nurses a wound on the back of his head in his study, Martha rushing in to make sure he is not harmed. Seeing all is well she begins to tidy his things whilst Smith recounts to Joan his dreams, wherein he is a man hiding from someone, he dreams he is a man with two hearts. Joan takes her stethoscope and examines his chest, playfully confirming he has only one.
He presents her with a journal of his dreams; a diary filled with scribbled writing and drawings of all manner of creatures some human. Martha looks on keenly and follows Matron out, trying to prevent her from reading the book, but to no avail.
In one of the school dormitories sit three boys, Baines, Hutchinson and a younger boy named Latimer. Hutchinson reads a letter from his father, and Latimer correctly manages to pre-empt that he has been stationed in Africa, despite knowing nothing of the man himself. He admits that he has in the past managed to predict things before knowing them, but the others ignore him. Baines decides to retrieve some concealed beer in the woods, and hurries out of the window.
That night Martha and Jenny sit outside the local pub, Martha somewhat annoyed at not being allowed inside with the men, and takes refuge in the fact she will be leaving in a month’s time. Suddenly she sees a bright green light in the sky, but Jenny denies it. However, in the woods not far away Joan, who is walking alone, is suddenly bathed in a vivid green light, which proceeds to scan the surrounding area like a searchlight.
Joan hurries to the pub, were Smith joins her. Together with Martha and Jenny they see another light falling to Earth, which Smith claims is a meteorite. He leaves with Matron whilst Martha runs off to find where the light came down.
In the woods, Baines is distracted from his work by an eerie green light descending from the skies. He nervously goes to find it but finds himself in an empty field. Suddenly he is stopped in his tracks by an invisible wall, which glows to the touch. He manages to locate a gap in the surface and wanders inside, disappearing from view.
Moments later Martha and Jenny arrive but find nothing, and returns wearily to the school whilst inside the invisible structure, which appears to be a ship; Baines is interrogated by sinister bodiless voices. He asks to know what they look like and moments later a scream rings out. He arrives sometime later back at the school, an unnatural look on his face. He sniffs around the room as Latimer looks on curiously, shining his shoes.
The next day Martha cycles into the woods, arriving at an abandoned cottage in which stands the TARDIS. She steps inside to find the ship illuminated only by the central console, the walls surrounding it are dark. She remembers arriving in the ship, chased by some unnatural force. She recounts the Doctor’s words to her:
“Martha, this watch is me”
He had explained to her that the creatures were chasing him, the last Time Lord in existence. To avoid them he had to become human. He used a helmet that descended from the ceiling, the chameleon arch, to change his own biology and store what made him a Time Lord inside the watch.
She looks up at the device still suspended from the ceiling in the darkened ship and she remembers his screams of agony. His cries of pain that rang around the ship as a new life was set for him and all that he was became stored inside the watch.
Finally she moves over to the scanner, playing back the last recording he made for her before the change; a list of instructions for what to do whilst he remains human. She scans them but finds nothing regarding meteorites in the sky, and is left alone in the hollow room.
Back at the school Latimer calls on Smith to borrow a book. Whilst his teacher searches for the title the young boy sees the watch the mantle, he opens it temporarily as voices swarm around his head, and as Smith returns he places it in his pocket. He retreats back to his room and opens the watch, a bright light emitting from within and the voices returning.
Outside Baines appears to sense the disturbance, and when he returns inside he reports back to the ship that a source has been detected, and the soldiers must be activated.
In a field not far away a man named Mr Clark sees one of his scarecrows moving. Thinking it to be one of the schoolboys he reaches inside the lining to grab them, finding only a handful of straw. Bemused he looks at the figure, which grabs him as others like it spring to life across the field. On a road nearby a small girl with a balloon walks along, but is confronted by a scarecrow, who carries her away, screaming.
Back at the school Smith oversees the boys practising to fire machineguns at dummy targets. Latimer and Hutchinson arm the weapon, the former appearing to experience a vision of war, himself and his colleague fighting in the maze of barbed wire and mud. He observes his watches and claims that the “time is now”.
Breaking from his fantasy Hutchinson takes him away to be beaten, whilst Baines simply sniffs at his teacher, Smith. Matron appears from inside and Smith moves to speak to her, finding her upset by thought of her husband who was killed in war.
Together they leave the school and walk through the local town, discussing the idea of war, a premonition Smith appears to find in his dreams. Suddenly the teacher observes an accident waiting to happen, a piano being hauled to a first floor window is about to fall, a woman with her pram slowly walking into it’s path.
He grabs a cricket ball from a nearby by and throws it at some scaffolding nearby. It pushes the poles aside, upsetting a plank of wood on which lays a brick. The brick launches into the air and upturns a milk urn, which falls in front of the pram, preventing it from moving further into the space where the piano falls.
Smith appears marvelled by his own capabilities and suddenly finds the courage to invite Joan to the village dance. Soon they are walking through the fields together, discussing the character of the Doctor. Smith sees a nearby scarecrow and moves to correct it on it’s perch whilst Joan compliments him on his drawing, provoking him to mention his home in Gallifrey, a place she assumes to be in Ireland. Having finished correcting the scarecrow the two walk off, unaware that it turns to watch them go.
Back in his study Smith sits and draws Joan in his journal, eventually moving to kiss her. He begins to mutter some excuse but she kisses him again, as Martha enters unannounced and sees them. She flees back to the TARDIS to consult the Doctor’s instructions but finds nothing to explain what she should do.
“You had to go and fall in love with a human…and it wasn’t me.”
At the school, Latimer sits with the watch and listens to the voices, stooping to observe Baines, Mr Clark and the young girl with the balloon meeting on the other side of the grounds. On a road not far away Jenny is ambushed on her bicycle, surrounded by the animated scarecrows.
Soon she is inside the alien ship, Baines introducing her to his mother, a glowing green orb. He claims that she needs a body and suddenly a green gas emerges from the orb, overcoming the poor servant.
Smith and Joan prepare for the ball as Jenny returns to her quarters, where Martha awaits. She sniffs unnaturally as Martha confesses her concern about Smith, who is to leave the school in a few weeks. She begins to realise that Jenny is not herself and hurriedly leaves. However, Jenny draws an alien gun and pursues her, firing at her as she flees.
She returns to Smith’s room and tells him they have been found. She tries to find the watch but it appears to have gone. Smith believes her to be having some sort of breakdown and patronisingly explains the situation to her, only for her to slap him in an attempt to bring him round. He grabs her by the arm and pushes her outside, dismissing her from his service. He then returns inside, where Joan tells him that Martha was not lying about the watch, it has gone.
Martha runs outside, bumping into Latimer (who appears to have a subsequent vision of the same incident occurring in Martha’s own time zone). She hurries back to the ship and rummages in the Doctor’s coat, as Baines and Jenny arrive in Smith’s now-empty quarters looking for him.
Smith and Joan meanwhile arrive at the village dance, closely followed by Latimer. As they dance around the room Baines and Jenny continue to search the school, before Mr Clark produces the poster for the dance. Jenny smiles, her daughter is already there.
At the dance the girl with the balloon watches the entertainment as Martha arrives, unaware the scarecrows are watching from the surrounding fields. Inside she confronts Smith and presents the Doctor’s Sonic Screwdriver, ordering him to identify it. She tries to explain to him that he isn’t John Smith; he is the Doctor, the man from the journal.
Soon Baines, Jenny and Clark arrive, storming the venue and shooting anyone who disobeys their orders for silence. Martha orders Smith to be silent as Baines turns on him, realising that the Doctor has taken human form. Smith fails to understand and Baines threatens to shoot him if he doesn’t change back. Jenny and Clark grab Martha and Joan and point guns at their heads. Baines offers him the ultimatum:
“Your friend or your lover. Your choice.”