Man on fire - A.J. Quinnell (Creasy #1)

Known only as Creasy, he was hired to protect, not to kill. A battle-scarred, burnt-out mercenary, working as a bodyguard for the young daughter of an Italian industrialist, he thought he had lost the power of feeling. Until the girl's beguiling touch awakens in him the ability to love.

Then something happens, something so devastating that Creasy is consumed by a single-minded rage for revenge. And at a stroke he is transformed into the terrifying killing machine he was trained to be...

Goodreads 4.26