The Invisible Woman — James Patterson; Susan DiLallo

From New York Times bestselling author​ James Patterson, an undercover FBI agent investigates a family with suspected ties to organized crime -- by posing as their live-in nanny.

No one sees her, but she sees everything. Elinor Gilbert was once a young woman with a thriving career at the FBI.
           Now decades past solving crimes with the bureau, she is personally and professionally forgettable. 
           Which is exactly what her former FBI boss needs. He disguises Elinor as a middle-aged nanny, and casts her as an agent on the inside of his investigation into a New York art dealer suspected of ties to organized crime.   
           But as Elinor pushes toward the truth, her superpower -- anonymity -- morphs into a fatal flaw. 
           The more the invisible woman integrates into her “host” family, the more dangerously memorable she becomes.