Hard Angel by Cole McCade

Unsettled tensions from the last case come to a head as Seong-Jae reveals his secrets — but will it be enough to repair the fractures in his relationship with Malcolm?
Especially when their only promising lead on the Golden Ratio Killer’s identity falls apart, along with any hope of returning home to Baltimore and to their life together.
When their primary suspect turns up dead…
…after attempting to kill the daughter of another suspect.
The Golden Ratio killer’s strange web of deception, double-backs, and doppelgangers grows ever more tangled, and as those twisted threads ensnare Malcolm and Seong-Jae, they find themselves pulled ever further apart. Not even Malcolm’s patience may be able to save them, their relationship a painful casualty of their job.
That doesn’t mean he won’t try.
But Malcolm’s desperate attempts to hold them together put them in the wrong place at the wrong time.
And that unfortunate coincidence?
Might just end both their lives.