London is sweltering and housemaid Flotsam longs for a break from the oppressive heat, although housekeeper Mrs Hudson remains unruffled. However, Baker Street is about to be consumed by an extremely weighty matter: the last Will and Testament of armaments tycoon Charles Belladonna. Belladonna left his considerable fortune to an only son who went missing, stolen from his cot, years before.

Now not one but seven young men appear, each claiming to be the long-lost heir. The tangled case draws the War Office's attention, and a demand for Mr Sherlock Holmes's assistance. Only the razor-sharp minds above and below stairs at Baker Street stand a chance of uncovering the truth and foiling the sinister forces at work.