Zero Zero by Jack Mars

When Agent Zero visits his doctor in Switzerland, hoping to salvage his deteriorating health, he is met with a shocking surprise: another agent who has been given a memory implant, just like him. And, just like him, this agent has deadly skills—and a singular mission: to kill Agent Zero.

Agent Zero has met his doppleganger, a darker version of himself.

Who is he? Who does he work for? Who chipped him? What secrets does he hold about Zero’s past? And why does he want Zero dead?