Erin Allin O'Reilly

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

With his friends knowing how sour he acts when he’s sick, Sheldon is nursed by Penny, who hasn't got a clue what she's in for.

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 (Keke Palmer) needs Shane's help.

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