Any Old Diamonds

I always include major spoilers (hidden), to help with my memory  issues. Read them at your peril! 

Entertaining heist/MM romance. Aristocrat and jewel thief with nothing in common. Alec, 2nd son of a duke, wishes for revenge on his father and asks jewel thieves to help him. The story covers the planning and execution of the heist, with them gradually finding common ground, and revealing more of their histories. But complete trust is never quite there, with consequences. Graphic sex scenes.

20 years ago, Alec's father murdered his mother in order to marry his mistress, who in turn murdered her own husband. Both are caricature baddies, with no redeeming features. Alec and his siblings have lived in comparative straitened circumstances after a final breach 10 years ago, when the duke's callous selfishness led to the death of Alec's sister. Alec asks Jerry and his partner to steal a diamond parure before it can be given to the duchess on her wedding anniversary. They get to know each other in order to be convincing best friends, and after some humiliating grovelling to his father by Alec, they are both invited to the fateful house party. Alec eventually tells Jerry about the murders, but doesn't tell him the big twist... it's all been a ploy to get the thieves to the house party in order to break a different safe than they have been planning, and get at proof of the murder of the duchess's first husband. It hits the fan when Alec fetches the private detective working in the house to Jerry's room to tell them what's really going on.