Keith, while not poor, has chosen to do work he loves in place of better-paying work, and cannot afford to travel to Polynesia. Keith infers that the metal box he secreted contained the diamonds, and he starts to investigate how he may retrieve them from the wreck. But, the solicitor handling the estate finds that the money has disappeared the evidence suggests that Keith's brother-in-law converted his wealth into diamonds to take with him abroad in order to evade export and currency restrictions intended to prevent capital leaving Britain. When the couple are killed in a shipwreck in French Polynesia, Keith becomes the permanent guardian and trustee of his niece (hence the title). Before leaving, they ask Keith for assistance in hiding a small box in the yacht's concrete ballast. The couple plan a long pleasure cruise in their small yacht before settling in British Columbia, meanwhile leaving their 10-year-old daughter with Keith and his wife. Keith's sister had married a wealthy naval officer, recently retired from service at the opening of the story. Stewart writes serial articles about how to build miniature machines in a magazine called the Miniature Mechanic, which are extremely well regarded in the modelling community - as is he.

The plot of the novel hinges on the actions of a modest technical journalist, Keith Stewart, whose life has been focused on the design and engineering of small and scale-model precision machinery. Shute died in January 1960 Trustee was published posthumously later that year. Trustee from the Toolroom is a novel written by Nevil Shute.

Trustee from the toolroom review