Roman Nesterov is an outstanding physicist who is very close to a scientific breakthrough. Perhaps in a few years people will learn to travel through time using the intertemporal corridors they have discovered. However, Roman does not suspect that he will encounter time travel much earlier. One night, a mortally wounded man appears in his bedroom. Before he dies, he gives Roman a mysterious black ball that allows him to travel to the past and future. Now the scientist has to answer the question - how to prevent the inevitable? After all, the person who arrived from the future is Roman himself, aged twenty years.