London 1946. An actress is murdered, not just on camera but in full view of a crowded film set. Only six people had an opportunity to administer the poison yet not one of them had a conceivable motive. As Evadne Mount, bestselling crime novelist, discovers, however, all six did have a motive for committing another, earlier, still unsolved murder yet, on that occasion, not one of them had the opportunity . . .