Cruel yearbook comments show Sam who's got his back, a favor he repays at graduation. Feelings for Izzie confuse Casey. Elsa asks Doug a key question.

A hard truth keeps Casey up at night. Sam experiences a rough season with Zahid -- and Paige. Elsa and Doug brace for their next chapter.

A rogue plan for Zahid leads to a last-minute mission for Sam, Casey, Paige and Abby. Meanwhile, Doug faces a major test and makes a pivotal choice.