When a highly eccentric, practical joke-loving and not very well liked millionaire Wilson MacLeish is killed when his new bi-plane explodes, Thomas, who had been working on a case for him, is summonsed to the reading of the will. Read out via a video-tape, the deceased millionaire leaves his ex-manservants some money, but leaves his relatives practically nothing, instead leaving his estate and wealth – fifty million dollars - to Thomas! MacLeish's relations are put out and angered by this, and Thomas takes up his new residence on the estate. On a second video-tape, MacLeish informs Thomas that before his death he had suspected that one of his relations is trying to kill him for his inheritance, and wants Thomas find out who. But it begins to seem that whoever may have been responsible for the millionaire's death is now trying to bump Magnum off too...