The Allgoods are a close family experiencing life's typical ups and downs: 18-year old daughter Joni (Mia Wasikowska) is heading off to Stanford University and starting to distance herself from her parents; 14-year-old Laser (Josh Hutcherson) is hanging out with a deadbeat friend who constantly leads him into trouble. The only difference is that this family has two mums. Jules (Julianne Moore) and Nic (Annette Bening) have been together for years, deeply in love, and had both children through artificial insemination.
This loving but strained home life is thrown into comic disarray when the kids track down their biological donor Dad, Paul (Mark Ruffalo), and invite him home for dinner. Paul is a bachelor whose sudden longing for a family introduces an interesting sexual dynamic to the not-quite-ordinary equation of the Allgoods. At first Joni is so happy to have a cool, handsome dad like Paul. But soon enough she comes to realise that Paul is fun-loving but lacks self-control: and chaos reigns.