Summer, 1915. As Zeppelins rain death upon the rooftops of London, eminent members of society begin to behave erratically: a Member of Parliament throws himself naked into the Thames after giving a pro-German speech to the House; a senior military advisor suggests surrender before feeding himself to a tiger at London Zoo; a famed suffragette suddenly renounces the women's liberation movement and throws herself under a train.
In desperation, an aged Mycroft Holmes sends to Sussex for the help of his brother, Sherlock.
Mann opens more strongly than he closes in his second Holmes novel (after 2013's Sherlock Holmes: The Will of the Dead). In 1915, Watson is feeling the butcher's bill of WWI personally. His nephew, the last of the family line, was killed in France, just "another forgotten face, another entry in the tally chart of the dead." He gets a welcome distraction from his personal woes when he's summoned to Victoria Station, asked by Holmes to help with a new case. London has been beset by a series of odd suicides: a British Army officer threw himself into the tiger enclosure at the London Zoo, a suffragette jumped in front of a train, and a Member of Parliament plunged himself into the Thames. All three high-profile victims opposed British involvement in the war. The probe takes an odd turn when a search of MP Herbert Grange's belongings turns up some portraits of the politician featuring the images of bizarre gaseous auras. The solution doesn't match the cleverness of the setup, and some of Holmes's deductions are less than convincing.