The team is joined by the FBI's assistant director of national security in a quadruple homicide case in St Louis.
Sheldon has a song stuck in his head; despite their awkward date, Amy asks Dave over for dinner; Koothrappali and Wolowitz are obsessed with a fan of their band.
Andrew and Philip learn that the destruction caused by their last mission requires their return; Simon Z is ultimately compelled to face his past.
Jesus and the disciples undertake a dangerous journey to the Decapolis after Andrew and Philip return with news of a crisis in the area.