Hilary Craven, a deserted wife and bereaved mother, is planning suicide in a Moroccan hotel, when she is asked by British secret agent Jessop to undertake a dangerous mission as an alternative to taking an overdose of sleeping pills. The task, which she accepts, is to impersonate the wife of Thomas Betterton, a nuclear scientist who has disappeared and may have defected to the Soviet Union. Soon she finds herself in a group of oddly-assorted travellers being transported to the unknown destination of the title.