Penny's ex-boyfriend Zack learns that he is infertile, so he asks Leonard for help; Koothrappali attempts to mend things with his ex-fiancee Anu.

Cast: Johnny Galecki, Jim Parsons, Kaley Cuoco, Simon Helberg, Kunal Nayyar, Mayim Bialik, Melissa Rauch, Shay Ali, Chip Chinery, Brian George, Rati Gupta, Lindsey Kraft, Brian Thomas Smith