Jack McCaskin is the former husband of high school teacher Danielle McCaskin. Danielle had an affair with Dr. Grant Tyler, a notorious womanizer, which was caught on tape. When Grant was later murdered in a fatal motorcycle sabotage, Jack was a suspect especially due to his rage at Grant over taking his wife from him.
However, Danielle was having an illegal affair with Grant's teenage son Keith, who she tried to flee the country with. Keith was revealed to be Grant's killer, in a prank gone wrong out of revenge for having sex with Danielle when Keith wanted her to himself.
After Danielle took a guilty plea to spare Keith jail time, and she was revealed to be pregnant with Grant's baby, Jack divorced Danielle out of horror and grief. (CI: "Tru Love")