Agnes Brown has family troubles to contend with: her son Dermot has fallen out with Maria Nicholson, his long-term girlfriend, and Grandad is feeling poorly. After a sleepless night, Mrs. Brown decides to try to sort out Dermot and Maria's problem by giving Maria the benefit of her advice. But her heart-to-heart with Maria only succeeds in making the dispute worse.

Agnes Brown worries that her family is keeping too many secrets when Cathy will not reveal any information about her new boyfriend, Mark will not confess why his wife has thrown him out and Dermot lies to his fiancee's parents about the status of his job

Agnes becomes concerned when Dermot announces he wants to ask his childhood friend Buster, a known criminal, to be his best man. Mrs Brown is distracted when her neighbour Winnie's husband is rushed to hospital, leaving her son trying to raise money for his wedding by becoming embroiled in a money-making scam with his friend.

Agnes is disappointed when she discovers she is not invited to Maria's hen party because she is too old, so she and Winnie decide to crash the event, but end up in the wrong venue. She invites Maria's mother round for dinner and is so nervous about impressing her that she gets drunk and the evening descends into chaos.

Dermot's pre-marriage nerves get the better of him and he locks himself away in a cupboard, so it is up to Agnes, Fr Quinn and best man Buster to try to calm him down. Meanwhile, Rory tells his mother he is gay.