Tegan and Turlough have been separated from the Doctor in Russia in 1904. They take a train to meet him in St Petersburg. They are accompanied by Sasha, who has an important message to bring. Before the train departs, Peter, a fellow agent of Sasha's, is killed.
When the passengers are crossing Lake Baikal, Sasha "falls" overboard. He is rescued, but is dying. Before he dies, he passes his message on to Tegan. Tegan is suspicious of every passenger, even Turlough, but especially of Fedotik, who often seems to be watching her.
Someone vandalises her and Turlough's room, searching for something. Someone seems to know that Tegan has the message that Sasha was supposed to send.
When Bazarov doesn't show up for breakfast, Tegan is suspicious. She and Turlough ask Rodya to open his room, but inside they find that not only has Bazarov's room been vandalised as well, but also Bazarov has been strangled.
Tegan and Turlough hatch a plan to catch the murderer. Tegan pretends to be asleep, while Turlough is out of the room. The murderer comes to their room and tries to suffocate her with a pillow, but she scratches his neck. The murderer gets away, but should have scratch marks on his neck. Unfortunately, it's winter and everyone is wearing a scarf.
As the train nears St Petersburg, Tegan sees Rodya near the open train door. She stumbles, and he steadies her. She notices scratch marks on his neck. He tries to throw her out of the moving train, but they arrive at the station. He escapes, with Turlough yelling for someone to stop him.
Rodya is caught - by the Doctor. As Tegan and Turlough meet up with him, Fedotik approaches them. He is one of Sasha's fellow agents. Tegan gives him the message - "Gudok" - which gives Fedotik the information he needs.
- Fifth Doctor
- Tegan Jovanka
- Yevgeny Petrovitch Bazarov
- Madame Ranevskaya
- Mademoiselle Varya
- Turlough reads Crime and Punishment by Dostoevsky.
- When crossing Lake Baikal, the passengers ride the Baikal while the train is transported on the Angara.
- Tegan recites Beatles lyrics in her head to keep awake, getting all the way up to The White Album.
- Vladivostok is under siege by a Japanese fleet.
- Tegan mentions the Wright brothers.
- Varya is supposed to practice piano every evening.
- The daughter of the ambassador to China would have travelled on the train if she had not contracted typhoid.
- The journey takes them past the Amur River, the mountains of Mongolia, Ulan Ude and Ekaterinburg.
- "Gudok" means Signal, the newspaper of the railwaymen.
to be added