Assassin Eighteen by John Brownlow

Ian Fleming Steel Dagger Award Winning-Author of AGENT SEVENTEEN
"John Brownlow is a master of suspense." - Jeff Abbott, New York Times bestselling author of Traitor's Dance
I am waiting for someone to kill me. Tonight would be a good night for it.
Agent Seventeen, the most infamous hit man in the world, has quit. But whoever wants to become Assassin Eighteen must track him down and kill him first. So when a bullet hits the glass inches from his face, he knows who fired it-doesn't he?
It turns out that the sniper isn't the hardened killer he was expecting. It's Mireille-a mysterious silent child abandoned in the woods with instructions to pull the trigger. Reuniting with his spiky lover, Kat, Seventeen has to protect Mireille and discover who sent her to kill him and why. But the road he must travel is littered with bodies. And the answer, when it comes, will blow apart everything Seventeen thought he knew.
"The most action-packed spy thriller that fans of the genre will read this year." - Irish Examiner
"Brownlow is an accomplished screenwriter, and it shows in his style." - Financial Times