The main characters are the narrator (Dick), who is a composer, and John Sinclair, a physicist; they were at school and at Cambridge University together.

They happen to meet at London airport as Dick returns home after conducting a premiere of a composition of his in Cologne, which got a mixed reception.

In California John meets other scientists in the project; it seems the space probe is detecting modulated radiation, i.e. signals, coming from the Sun.

John, later talking about this with Dick, is interrupted by news that Los Angeles has been destroyed; this is assumed to be so because radio signals from there have ceased.

They land in England; it is the present day there (although a month later than expected) but in France it is 1917, and the British government is trying to stop World War I. John thinks that the Sun was sending information in order to make copies of parts of the world; the odd events during their holiday were when he and Dick were replaced by copies.

John and Dick join an aeroplane excursion: in Russia, they find only a flat glass surface; Greece is in classical times.

Dick and John are shown a documentary film, covering the thousands of years since 1966, during which there were several crises where humanity became almost extinct, followed by a re-emerging civilization.

After meeting some government ministers in the London of 1966 who are considering how to deal with the situation in the France of 1917, which is in the midst of World War I, John Sinclair (in the last few pages of Chapter 7) talks to Dick about his theory that might explain what has happened.