She walked away from him while he was on bended knee at the prom when they were eighteen.
Without explanation.
She came back twelve years later as District Attorney for the district he served in as a deputy sheriff. Cassidy Osborne brought her ex-husband, the judge for Hunter McKay's district, upon her return. Along with her son, who plays baseball on the team Hunter coaches.
Throw in some gun happy criminals and enough revenge motivation for everyone to have some; then force the three adults to work together whether they want to or not. In the deep South, you can consider the fuse lit.