Erin Allin O'Reilly

Penny hosts a Halloween party, putting Leonard, Sheldon, Wolowitz and Koothrappali through a new test of their social skills.

Without having a clue what she has let herself in for, Penny volunteers to nurse Sheldon when he's sick. However, his friends know how miserable he is when he's ill and stay well away from him.

Bailey asks Richard to join her on the case of a lifetime; Meredith decides to hire a research assistant; Callie shocks Derek; a young pregnant woman needs Shane's help.

McGee's girlfriend, Delilah, turns to the team for help when she finds a break in a controversial case, and McGee considers asking Delilah to move in.

The NCIS team consult with three cyber-terrorists they imprisoned after a citywide Internet shutdown, the week before Christmas. McGee reflects on the case and Gibbs' infamous rules as he pens a heartfelt letter to his father.

A frightening being is summoned, one that even the possessed Sister Mary Eunice is afraid of. As Kit and Lana resort to desperate measures, a despairing Sister Jude finds she can no longer run from her past.