Ruby accepts the Doctor's invite to travel with him. First stop, some 150 million years into the past which results in a slight accident so the Doctor decides they should try another, random destination in time and space. Asking Ruby to think of a number she comes up with 21506 and so the Doctor sets the TARDIS to travel into the future.

Materialising inside a spacestation, the Doctor and Ruby begin to explore, first of all discovering that some parts need repairing and also that there is a monster roaming around. They manage to escape from the monster using a travel tube to take them to another level. There they find babies in stasis: the station is a baby farm for the purpose of founding new colonies and is currently near the planet of Pacifico Del Rio. However, some of the babies have revived and with the help of the ship's computer are doing their best to maintain the station. Despite that, and in addition to the faults and the monster, the station is too far from the planet to fulfil its function.

In 1925 a boy is taking a piano lesson: first there is a note, then a tune and then a melody. As the teacher, Timothy Drake begins to play some Beethoven and talk about the composer it becomes clear that the boy, Henry is bored. Drake mentions another tune known as the devil's chord, banned by the church in medieval times as it was believed to allow the devil to enter a room. This interests Henry and so Drake begins to play it until the piano lid slams down. He hears a knock from inside the piano as if someone is inside it, which is clearly impossible. Looking inside, Drake is startled to find that there is someone inside the piano. Dropping the lid he then sees the same person sitting at the piano next to Henry. This new arrival introduces themselves as Maestro and they are music.

The Doctor and Ruby arrive in London, November 1963 - next to the famous crossing on what will be named Abbey Road. Visiting EMI recording studios they witness The Beatles recording, except the song is quite bland. Popping into another studio they watch Cilla Black recording a bland song. In another studio, an orchestra plays dreary music. Its as if something has drained the life out of music. If uncorrected, the world will be destroyed: the Doctor shows Ruby Earth 2024 if Maestro is not stopped.

Two survivors from Patrol B, one injured, are making their way back to basecamp less than a mile away. They make their way carefully as there is a minefield in the area, and an ambulance ahead of them. Trying to avoid the ambulance Carson, the uninjured man scouts ahead but falls into a crater and steps on a landmine. The detonation activates the ambulance. The injured man, Vater, his eyes bandaged stumbles around until the ambulance intercepts him, makes its diagnosis and deems the 4-week recovery period as unacceptable. Despite Vater's pleadings, the ambulance requests that he leave a final message for his next of kin.

The TARDIS materialises on the battlefield and the Doctor informs Ruby that he can hear someone in trouble. Telling Ruby to stay, the Doctor runs out, makes his way through a crater and steps on a landmine. Ruby leaves to find the Doctor and despite his assurances that everything is fine she makes her way to him. Standing as still as he can, the Doctor asks Ruby to describe the landmine. He instructs her to look around for a rock or some object that he can use to help him redistribute his weight. Ruby finds a cylindrical object she calls an urn. The Doctor realises its a smelted version of a person, probably the scream he heard, essentially someone's remains. It is acceptable as counter weight but Ruby must be careful in giving it to the Doctor as the landmine is a smart mine. The landmine will convert him into the explosive unless he can keep his adrenalin levels down. Any excitement, fear that would trigger an adrenalin rush will cause him to detonate.

The TARDIS materialises on a cliff on the Welsh coast. The Doctor remarks on Wales and begins to talk about Roger Ap Gwilliam, the worst prime minister until he realises that isn't until 2046 and Ruby is from 2024. As his foot comes down, the Doctor realises he has stepped on a fairy circle made out of string and charms. While the Doctor apologises, Ruby examines some of the messages left within the circle. Looking up, she finds herself alone. Assuming the Doctor has returned to the TARDIS, Ruby finds the door locked, even when she tries the key. Seeing a woman nearby, Ruby asks her if she has seen the Doctor. Bizarrely, as Ruby approaches the woman she appears to maintain the same distance from her.

Ruby heads inland and notices the woman is following her, keeping her distance. When Ruby meets a hiker she is directed towards a nearby village. In return, as the hiker will be passing the strange woman Ruby asks her to pass on a message: she is sorry for any trespass she has caused. As Ruby watches, the hiker walks towards the woman. They have a conversation which appears to strike fear into the hiker who then runs off.

As bombs rain down on Manchester 1940, the Flockharts staying at The Queen's Hotel ponder on whether or not this is the end of everything they hold dear. The Doctor comes through a doorway, with a ham and cheese toastie and a pumpkin latter. He departs as quickly as he entered. Basil Lockhart tries the door and finds it locked.

On the Orient Express travelling through Italy in 1962, Sylvia Trench sits in her compartment reading over a letter she is writing when the Doctor enters and then departs.

Edmund Hillary and his team are at basecamp on Everest in 1953, when the Doctor enters through a flap at the back of the tent. Again he departs as quickly as he arrived.

Joy Almondo checks into the Sandringham Hotel in London, on Christmas Eve 2024. Remarking to a fly in her room that she thought she was going to be lonely, Joy is astonished when a Silurian, carrying a suitcase, enters through a previously locked door. And then the Doctor enters the room.

London: Christmas 4202 and the Doctor arrives at the Time Hotel where guests can pass through doors into different points in Earth's history for mini-breaks. He is there for fresh milk for his coffee: his presence attracts the attention of Trev Simpkins who wants to know if he is a guest. As he returns to the TARDIS, the Doctor realises he has two mugs of coffee and so hands one to Trev. Once inside the Doctor leaves his coffee, removes his dressing gown, puts on his jacket, picks up the sonic screwdriver and leaves: a guest with a suitcase cuffed to his wrist has checked in but now is standing there, not doing anything. Recruiting Trev to keep watch in the lobby, the Doctor orders a hamd and cheese toastie and a pumpkin latter so, as room service, he can investigate the potentials rooms the man with the suitcase wants to access, after all the best way to folow someone is to get there first

The receptionist informs the man with the suitcase that the rooms are currently in use so he should wait in the bar. There, the man asks the barman to put his suitcase behind the bar. The cuff automatically detaches from the man and then reattaches to the barman. The man reels and wonders what has happened to him. The barman calmly tells him to relax as he will be dead shortly.