Benoni’s Defence by Stockton Smith

Artie hires private detective Cass Fisher to find the killer. She's unprofessional, unpredictable, and the best detective with an ad on Facebook marketplace. For what it's worth, Artie's fiancee thinks she's taking advantage of him.

But when Cass's delusional theories start panning out, Artie wants in on the excitement. After visiting a weapons expo undercover, they find themselves pursued by enemies who will stop at nothing, including murder, to cover up a conspiracy at the highest rungs of power.

The clock is ticking. If Artie can't figure out who's pulling the strings, he and his fiancee are dead!