The Templeton brothers--Tim (James Marsden) and his Boss Baby little bro Ted (Alec Baldwin)--have become adults and drifted away from each other. Tim Templeton is a stay-at-home dad for two adorable daughters, while Ted is a big-shot CEO. They come together in an unexpected way when they take a magical formula that transforms them into babies for 48 hours. Joining forces with Tim's secret-agent daughter, they must go undercover to prevent an evil genius from turning fellow toddlers into monstrous brats.