As detective Paul Temple turns his hand to playwright, his leading lady Iris Archer pulls out shortly before the play is due to open and declares that she is heading for France.
However, shortly after her disappearance Paul Temple receives a guest at his Scottish holiday home - none other than that of Iris Archer.

The mystery deepens as Temple is asked by a young man to act as postmaster in delivering a letter. Meanwhile someone acting under the codename of Z4 seems to have control of events. Could this be Doctor Steiner, and just who is he? It is all up to Temple …