Requiem for a Glass Heart — David L. Lindsey

REVENGE CAN BE ECSTASY.

Irina Ismaylova is a sexual assassin, luring men and women to her bed...and their death.  From St. Petersburg to Paris, she kills not for money or for pleasure, but under orders from the Russian mafioso who holds her in thrall.  Desperate to buy back what is left of her shattered life, Irina must carry out
one last mission....

Cate Cuevas is a special agent in Houston's FBI office.  Devastated by her husband's death--and his betrayal--she has plunged into the most dangerous
assignment of her career.  But to succeed, she must form a secret and profoundly intimate alliance with the enemy: Irina Ismaylova.

Two women.  One a cop.  The other a killer.  

For these two there is no right, no wrong, no rules.  

Only the truth...and terror.