Third Degree by Greg Iles

Laurel Shields has been married to Dr. Warren Shields for a dozen years but they've started drifting apart. She begins an affair with Danny, the father of one of her special-needs students. As our story opens, Laurel is dismayed to find she is pregnant. When she gets home from her teaching job, she finds her husband in a frenzy, waving around an anonymous letter that is clearly from her lover, and demanding to know who he is. And so begins the knuckle-biter Third Degree.

Soon her husband is holding Laurel hostage. She finds out that Warren's partner's actions have led to a fraud investigation of their practice. (An anonymous phone call to Warren had advised him to search his house for incriminating evidence that the partner had planted there, which is when he turned up the love letter.) The tension ratches up as their two young children return home from school and also become hostages. A member of the sheriff's department has a long-standing grudge against the doctor and would be happy to settle it with a bullet. And secrets that Warren has been keeping from Laurel come out, which add a whole new perspective to the proceedings. Then irony of ironies, Danny ends up on the hostage negotiation team.  It's all very tense -- and kind of sad.

If you're in the mood for a good thriller this summer, try Third Degree.