Paul Temple agrees to write a play for actress Iris Archer. However, shortly before the play is due to open, she pulls out. Then after telling everyone she is off to France, she turns up at the Temple's Scottish holiday hotel. 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 ...