Sarah and David are the last of the group to succumb to hiring a nanny but, when confidences are broken on both sides, romantic betrayal and revenge lead to all-out domestic warfare. And trouble awaits them all when the nanny mafia moves into action.

Who is Stuart having an affair with? The nannies investigate. Sarah finds herself in an increasingly fraught entanglement with Ben and Katherine.

Beattie and Stuart's marriage is deteriorating, and Lisa is out for revenge.

In the final part of the dark comedy, Sarah and David find their marriage and friendship tested to the limit while the "nanny mafia" plot to save the day.