Hyde

Book four in the Sterling Files series.
To be a hero, he had to sacrifice his soul. Now more beast than man, Dr. Henri Édouard pushed the limits of science in an effort to save countless lives from a drug he foolishly designed for one purpose — to create an invincible soldier.
In the aftermath, the government seeks the formula and Henri is on the run. But he cannot outrun himself.
Sterling wants to reach Henri before the drug destroys him. Dr. Alison Cunningham must save him no matter the cost and is willing, for her own reasons, to risk her life for his. What she didn't count on risking was her heart. Though the clock is ticking, Henri and Alice find that love is the most dangerous drug of all.