Petteril's Ladybird (Lord Petteril Mysteries #3)

An earl’s son, shot in the home of his mistress…

Lord Petteril, with his redoubtable assistant April, is called back to London to help prove the innocence of his friend, Percy Austen, who is suspected of murder.
Percy was once the lover of the victim’s mistress, and his pistol was found at the scene of the crime. However, there is an embarrassment of other suspects, all of whom seem to have a tangled relationship to each other as well as to the dead man. And more than one is connected to April’s past.

As Petteril and April investigate among the aristocracy of Mayfair and the villains of St. Giles, their relationship reaches an unexpected crisis of its own. Is their friendship strong enough to withstand honour as well as convention? Or will this mystery part them for good?