After the sudden murder of a man at a cricket game, a mysterious omnipresent organisation known only as the Mark of the Crescent catches the attention of Department Z.
The strange attacks are increasing in frequency and the mark is everywhere. In buses, trams, trains, in the streets, in shops, in private houses, those tell-tale marks were seen. Members of the police force, errand boys, dustmen, owners of exclusive shops in the West End, soldiers and sailors had them. Clerks and navvies had them.
Starting at the country estate of Greylands, Chief Gordon Craigie and his team of agents are hot on the trail of the organisation’s leader. But where does the trail lead? And can the Department find out before it’s too late?
The Mark of the Crescent is the fifth book in the Department Z series, and was originally published in 1935.