The Bloodline Feud: an omnibus edition of the first two novels in Charles Stross's The Merchant Princes series
The six families of the Clan rule the kingdom of Gruinmarkt from behind the scenes. They are a mixture of nobility and criminal conspirators whose power to walk between their world and ours makes them rich in both.
Miriam, a hip tech journalist from Boston, discovers her alternate-world relatives with explosive results that shake three worlds. Now, as the prodigal Countess Helge Thorold-Hjorth, she finds herself ensnared in schemes and plots centuries in the making. She is surrounded by unlikely allies, lethal contraband, and most dangerous of all her family.
To avoid a slippery slope down to an unmarked grave, Miriam must build a power base of her own with unexpected consequences for three different time lines, including the quasi-Victorian one exploited by the hidden family.