Wicked Business by Janet Evanovich

Lizzy Tucker’s once normal life as a pastry chef in Salem, Massachusetts, turns upside down as she battles both sinister forces and an inconvenient attraction to her unnaturally talented but off-limits partner, Diesel.

When Harvard University English Professor and dyed-in-the wool romantic Gilbert Reedy is mysteriously murdered and thrown off his fourth-floor balcony, Lizzy and Diesel take up his twenty-year quest for the Luxuria Stone, an ancient relic believed by some to be infused with the power of lust. Following clues contained in a cryptic nineteenth-century book of sonnets, Lizzy and Diesel tear through Boston catacombs, government buildings, and multimillion-dollar residences. On their way they’ll leave behind a trail of robbed graves, public disturbances, and general mayhem.

Diesel’s black sheep cousin, Gerwulf Grimoire also wants the Stone. His motives are far from pure, and what he plans on doing with the treasure, no one knows… but Lizzy Tucker fears she’s in his crosshairs. Never far and always watching, Grimoire has a growing, vested interest in the cupcake-baker-turned-finder-of-lost-things. As does another dangerous and dark opponent in the hunt – a devotee of lawlessness and chaos, known only as Anarchy.

Treasures will be sought, and the power of lust will be unmistakable as Lizzy and Diesel attempt to stay ahead of Anarchy, Grimoire, and his medieval minion, Hatchet, in this ancient game of twisted riddles and high-stakes hide-and-seek.

This is a fun offshoot of the Stephanie Plum books - Diesel was part of the "Between the Numbers" books.  So it is fun to see him get his own series, I enjoy Lizzy but wish we saw more from Diesel's point of view as Lizzy is very much like Stephanie except instead of having a hamster she has Diesel's pet monkey and instead of being a bounty-hunter she hunts for missing artifacts (namly the 7 deadly sins) - this one is Lust.