It's the week of Dermot's fiancée Maria's hen party and Agnes Brown and her friend Winnie are so excited about going. until daughter Cathy tells her they are not invited because they are too old. Determined to attend, Mrs. Brown schemes to crash the event and show the girls that Agnes and Winnie are not too old to party. She thinks her luck is in when son Dermot tells her where the girls are meeting - down at local pub Foleys. However, when Agnes bursts into the pub in full hen party attire, it becomes clear that Dermot may have misinformed her. That night Agnes Brown mistakenly invites Maria's snooty mother Mrs Nicholson to dinner. Considering a second toilet to be the height of sophistication, Agnes has one fitted in one of the downstairs cupboards in order to impress her guest. Despite this, and despite drafting in Rory's cordon-bleu friend Dino to cook dinner, on the night Mrs. Brown is incredibly nervous, and turns to drink. With Mrs Brown increasingly desperate to impress, the evening descends into chaos as the drink takes hold, the aftermath of Agnes' hen party mistake plays out, and Grandad decides to go to the toilet. in the wrong cupboard.