The Retribution (Carol Jordan and Tony Hill #7) by Val McDermid.

From Goodreads:
There is one serial killer who has shaped and defined police profiler Tony Hill’s life. One serial killer whose evil surpasses all others. One serial killer who has the power to chill him to the bone: Jacko Vance. And now Jacko is back in Tony’s life – even more twisted and cunning than ever before.
My Rating: 🌟 🌟 🌟
This book had a lot of potential. Carol and Tony are moving their lives to a new chapter and moving closer to a proper relationship, Jacko Vance breaks out of prison and there is another sicko serial killer on the loose. Somehow, however, the author manages none of the story lines particularly well.
Everything about this book is grand but it’s far from great. The twin stories of the new killer and Jacko’s revenge spree were very underdeveloped and really should have been two separate books while the ending was shockingly sudden and verging on ridiculous with Jacko. Both stories felt like the author ran out of time, especially with the new killer. This story just finished very abruptly. Add in the complete overreaction by Carol towards Tony and the overall story left a bad taste.
The saving grace of this book is the development of the secondary characters, especially Paula and Stacey. The second story line allowed for this but I really would have preferred to see this happen in a separate book.
It’s a step in the series and worth reading but the next instalment needs to be much better to rescue the series.