Knave of Diamonds

Mary Russell's allegiances are tested by the reappearance of her long-lost uncle--and a tantalizing case not even Sherlock Holmes could solve.
When Mary Russell was a child, she adored her black sheep Uncle Jake. But she hasn't heard from him in many years, and she assumed that his ne'er-do-well ways had brought him to a bad end somewhere--until he presents himself at her Sussex door. Yes, Jake is back, and with a load of problems for his clever niece. Not the least of which is the reason the family rejected him in the first place: He was involved--somehow--in the infamous disappearance of the Irish Crown Jewels from an impregnable safe in Dublin Castle.
It was a theft that shook a government, enraged a king, threatened the English establishment--and baffled not only the Dublin police and Scotland Yard, but Sherlock Holmes himself. And, now, Jake expects Russell to step into the middle of it all? To slip away with him, not telling Holmes what she's up to? Knowing that the theft--unsolved, hushed-up, scandalous--must have involved Mycroft Holmes as well?
Naturally, she can do nothing of the sort. Siding with her uncle, even briefly, could only place her in opposition to both her husband-partner and his secretive and powerful brother. She has to tell Jake no.
On the other hand, this is Jake--her father's kid brother, her childhood hero, the beloved and long-lost survivor of a much-diminished family.
Conflicting loyalties and international secrets, blatant lies and blithe deceptions: sounds like another case for Mary Russell and Sherlock Holmes.