I read this over week ago, but haven't had time to review until now.
At the end of Case Histories Jackson Brodie ran off to France with his inheritance for an early retirement. One Good Turn sees him back in the UK two years later. He arrives in Edinburgh for the festival to see his girlfriend Julia in a play and finds himself in the middle of police investigations and in the cross-hairs of Louise, a no-nonsense female officer.
The plot sees several seemingly unrelated crimes: a fit of road rage, the body of a girl washed up on the beach, and the unscrupulous practices of a business man, but they all prove to be connected. Atkinson richly illustrates the lives of these characters, making each one come alive, not just Jackson. One of the best characters is Martin, a soft-boiled crime writer who is hapless, but sympathetic. Atkinson clearly has fun writing passages from Martin's formulaic stories. Gloria the middle aged wife and Tatiana "Jojo" the dominatrix form an interesting alliance to find their own brand of justice. The introduction of Louise as a match for Jackson was a good move as well, I hope that's developed more in the next book. I never liked Julia as his romantic interest.
This is a rare example of the sequel being superior to the original. Atkinson improves on her ability to balance multiple stories and bring them all back to Jackson, the linchpin. The way all the cases end up intersecting is creative and intriguing. She makes you interested in all their lives, even when they make mistakes, even when they break laws, they still have your interest, your sympathy. Rather than the unrelated stories of Case Histories, One Good Turn brings everything together to make a more cohesive story.