The team hunts a suspect who impregnates young women and has them give birth before murdering them.
When the gang helps Barney's mother move, they learn that she has lied to him about events throughout his life. Robin oversells Ted to a blind date.
The gang realise that their partners bear some resemblance to their parents. Meanwhile, Barney and Nora's romantic evening is ruined by a string of disasters.
Barney is determined to show his dad that it was a mistake to have given up his former life of wild partying, drinking and sleeping around.
The hospital is locked down when a newborn disappears from the nursery; new insights about the team's personal lives, relationships and regrets surface.