Costumed patients create a challenge for the doctors; Derek and Ben work on a new surgical technique; Richard asks a resident to perform his next surgery, angering Bailey.
When a hero emerges from the wreckage of an explosion in Indianapolis, the BAU team members must protect him, as they try to identify the person responsible before more bombings occur.
Following McGarrett and Wo Fat's escape, gunmen hit Five-0 headquarters; McGarrett must turn on his own in order to find Catherine.
The team follows a scientist who may have been targeted by terrorists, hoping to link those same terrorists to a presidential assassination plot.