Raven's Conspiracy: Book 4, The Guardian Series

Cockroaches aren't usually the best communicators, but when the proprietress of the Gardens of G ap and Gomory is strip-searched, thrown in a dungeon and starved during a routine business trip, she learns from the fat-bodied insect that her former associates consider her a traitor and will likely execute her in the morning.

Our heroine's troubles don't end there, either. In Gomory's absence, well-meaning employees accidently destroy her office and records, release a witch who'd been held spellbound for thousands of years, and manage to lose seven magical medallions created by Merlin. Good thing the aging sorcerer himself decides to drop into her cell to rescue her...right?