Winter's Child by Margaret Maron (2006)

It's one month after their wedding, and the future looks bright for Judge Deborah Knott and Sheriff Deputy Dwight Bryant until a disturbing call from Dwight's 8-year-old son Cal calls him back to Virginia.When he arrives, he is shocked to find that his ex-wife has left the boy alone for almost 24 hours. Worse, as Dwight tries to confront her, she takes the child and leaves town without a word. As Dwight embarks on an all-points search, Deborah hurries to his side. But will they be able to work together to decipher the ex-wife's motives and, more importantly, will they find young Cal before he comes to harm?