In Deepest Dark; In Frankenstein's Shadow Benjamin N Thurber

When a man with no past drops in on the lives of a small FBI team, none of them realize the rollercoaster they are in for. When he slowly reveals why he rides in a car that can produce, literally, anything with an RV that would rival most labs, they know he's on a mission, one to avenge the death of a loved one, to protect others from the same, and they become something stronger than before, something nobody expected. They become a family.