Penhale Wood by Julia Thomas

Penhale Wood is the second novel by Julia Thomas and the first starring Detective Rob McIntyre.  Rob has gone to London to visit with his brother and family for Christmas. He is feeling lost and considering leaving the police force since the "love of his life" Allison left him without a word after ten years together.   When he arrives, he finds that his sister-in-law has an emergency situation and the family has left London.  Rob stays over and is accosted by Iris Flynn whose three year old daughter was murdered by the live-in nanny a year ago.  Iris is determined to find Karen Peterson and make her pay for her daughter's murder.  After leaving the child on a river bank at Penhale Wood,  the nanny disappeared and was never found.  Since the funeral, Iris, her husband and other two children have been living with her sister in Australia.
Iris's husband  has also stayed in Australia which leads readers to question their marriage. Iris demands Rob drop everything and find Karen.  Rob thinks she is hiding in London and will be impossible to find.  There has been a recent development in the case-a psychic has reported she has seen the killer through the eyes of someone in the same room as Karen.  She is able to describe this person to the police sketch artist, but it does not look like Karen.  Again the trail seems cold, but Iris pushes on determined to find her daughter's killer with or without the detective.
There is a side story concerning Rob's ex Allison and her burgeoning career as a crime writer.  As the two stories come together, the tension and the clues ramp up.  Who is Karen Peterson and why are the police unable to find her?  Why and how is Allison involved?  Why was Sophie killed?  Well you will just have to read the book and find out!