The plot concerns the newly independent fictional African nation of Ng'ombwana, whose president and Alleyn went to school together, and a series of murders connected to its embassy in London.

I've saddled myself this time with a complicated and hideously exacting mise-en-scene and am just crossing the halfway mark, full of black forebodings laced with pale streaks of hope."

The investigation, headed by Alleyn and his Scotland Yard support team of Fox, Bailey and Thompson and his Special Branch colleague Fred Gibson, is hampered by the diplomatic complications of a murder committed on "foreign soil" in an embassy, and it doesn't help that Alleyn's wife Agatha Troy is painting a portrait of The Boomer at his request, which she senses will be the magnum opus of her illustrious career.

Capricorn Mews is home to a deeply unpleasant cast of suspects with colonial Ng'ombwanan connections, all of whom attended the embassy reception and have been meeting in Sheridan's basement flat, to work for régime change.

The motley conspirators include Colonel Cockburn-Montfort, former head of the Ng'ombwanan Army, and his wife, both alcoholics, and an obese brother and sister, formerly wealthy business owners in Ng'ombwana, now running a small pottery in Capricorn Mews, "K & X Sanskrit: Pigs".