The irrepressible Mim celebrates turning 70 by writing a bucket list and dragging her reserved daughter, Fran, on a trip they never had to a theme park.

Mim has a plan to fund her bucket list by selling the contents of a time capsule buried at Cambridge, her alma mater, but Fran learns a secret about Mim's past.

Mim and Fran try to help on a trip to cousin Pat's when Gemma reveals that she doesn't want to go through with her wedding, the night before she is due to be married.

Mim lets slip a crushing deception, and Fran calls an end to the trip, but it looks like time might be running out for Mim to tell Fran the biggest secret of all.