Penny's ex-boyfriend Zack asks Leonard for help after discovering that he's infertile; Koothrappali tries to patch things up with his ex-fiancee, Anu.
Jeff is admitted to hospital after unwittingly eating Jen and Adam's 'special' cupcake, and resolves to eat healthier foods; Russell convinces Timmy to act as his wingman.
Christy begs Adam to take Bonnie back after she starts to drive everyone crazy with her broken heart after they break up.
Sabrina reunites Salem with his daughter, Annabelle, who invites Sabrina to be maid of honour at her wedding.
Jake and Terry goundercover to catch an infamous arms dealer at an illegal gambling club; Holt's gambling addiction resurfaces; Boyle buys a truck with a shady past.