John Sanford introduces assassins in his novel Hidden Prey. It starts with a killing of a Russian Rodion Olsehev. Carl Walther is a teenage boy who is taught to kill by his grandpa. He kills the Russian and while escaping sees a homeless bum, Trey, witness the killing. He sees her after she steals money from the dead Russian and is running away from the dead body. She somehow manages to escape the killer by slashing him with a pen knife.
Lucas and team are called to investigate as this is a high priority case, a Russian, Nadya is also sent to assist Lucas and report to the Russian government.
Nadya and her colleague do a parallel investigation on the murder with suspicion on the BCA. Nadya herself has different motives in pursuing the investigation.
This homeless bum herself improves her life drastically through the money stolen from the Russian. She tries to point the detectives in the right direction without revealing her identity.
Finally its revealed that the enemy is closer to home. How Lucas finds out the killer, how he stops certain elements from jeopardizing the investigation and how he catches the killer forms the story.
The novel keeps you enthralled and hooked to it till the very end.