Ticket Out by Michelle Diener

It’s the summer of 1963 and Gabriella Farnsworth is a newly-minted London traffic warden. She’s used to temper tantrums, swearing, and threats, but finding a dead body is an entirely new low.

She isn’t interested in getting more involved than she already is in the investigation into the man she found’s death, but when, a few days later, she stumbles over a second body lying feet away from where she found the first, she can’t avoid it.
She knows the streets of her route, knows the people on them, but she is absolutely astonished when New Scotland Yard discovers the art gallery near where she found the bodies is a front for mixing up a new psychedelic drug.
Suddenly, the reason for the killings starts to make sense, but what neither she nor the New Scotland Yard detective assigned to the case understand is that the killer’s agenda is more complex than a drug turf war, and by the time Gabriella works it out, it just might be too late . . .