Bath Haus by P. J. Vernon

Bath Haus is a scintillating psychological thriller with an emotional punch about truth, trust, and the devastating cost of betrayal.
 
When does the betrayer become the betrayed... Oliver Park, a recovering addict finally has everything he ever wanted: sobriety and a loving, wealthy partner in Nathan, a prominent trauma surgeon.

Despite their difference in age and backgrounds, they've made a perfect life together. With everything to lose, Oliver shouldn't be visiting a gay bathhouse. But he does and a line is crossed.

Inside, he follows a man into a private room and whatever happens next, Nathan can never know. Then, everything goes horribly wrong, and Oliver barely escapes with his life. He races home in full-blown terror as the hand-shaped bruise grows dark on his neck.

The truth will destroy Nathan and everything they have together, so Oliver does the thing he used to do so well: he lies…
 
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'Breathlessly twisty. Brilliantly addictive.'  - C.J. Tudor