Murder In Training by Diane Weiner

When a retired teacher and her bestie join a training class with the goal of walking a breast cancer charity race, they run into a speedbump when a member of the group is murdered in the park. He had no shortage of enemies. Blackmail, harassment, and smuggling top the list of motives. Susan and Valerie both have detective daughters who for once request their mothers’ help. Their inroads with the training group put the amateur sleuths in a position to gather and pass along information. Meanwhile, Susan receives a mysterious gift on her doorstep and has no idea what it is or who sent it. Valerie questions whether or not it’s time to start dating again after losing her husband. And Susan’s daughter has a secret of her own.