July 1910. Lady Hardcastle and her tireless sidekick Flo have finally embarked on a long-overdue seaside break. But just as they’re wavering between ice creams and donkey rides, their fellow guests start to go missing—and the duo find themselves with a hysterical hotel manager and a case to solve.

The first to disappear is Dr Goddard, a scientist doing something terribly top-secret for the government. Gone too are his strongbox and its mysterious contents. By the time Lady Hardcastle has questioned the horde of international guests, her number-one suspect has been dispatched in grisly circumstances—and then the others start vanishing too.

As the case begins to look like a matter of national security, Lady Hardcastle takes advice from her brother in the secret service. But could there be an even more personal connection at play? To solve the case, Lady Hardcastle may face a shocking discovery of her own.