On Guard (The Eternal Dungeon, Volume 4) - Turn-of-the-Century Toughs, #4

"'Shall we allow criminals to roam the streets at will because we're afraid to take the chance of harming an innocent prisoner?'"A bloody knife from a crime scene becomes a mystery to be solved and a foreshadow of trouble to come. The ties forged between the noble-minded Eternal Dungeon and an abusive foreign dungeon have set off an unpredictable chain of horrific events, in which the love between two of the Eternal Dungeon's Seekers (torturers) will be tested to the straining point.
Caught in the middle of the struggle are Barrett Boyd and Seward Sobel, loyal guards who will find themselves questioning their most fundamental beliefs about the royal prison's ideals. Barrett must help his Seeker determine whether their mild-mannered prisoner is an attempted murderer. His friend Seward has pledged to guard his own Seeker against an assassin .