While on a stake-out to capture a strangler who is killing homeless women, Corrigan receives a blow to the head while struggling with a suspect, leaving him with a concussion which triggers sudden, unexpected bouts of enraged behaviour. But the suspect Corrigan took on isn't in fact the strangler, and with the real killer still on the loose, Hooker and the team must track him down before he strikes again. Corrigan's refusal to acknowledge his condition doesn't exactly help matters.