It's 1971 and the "Class of 65" are gathering at a seaside resort for a reunion weekend.

Frankie 'the fingers' Fuller and his intellectually challenged sidekick John 'Duggs' McGee book into the Grand Hotel with the sole intention of tunnelling through to the bank next door. Having asked for Room 1 or 2, their first disappointment is to find that Reception have misheard their request and they have been placed in Room 102 on the third floor instead. It gets worse when they discover that the school reunion party in the hotel that weekend is their old school !

'Nice guy' Tony meets up with his childhood flame Karen at the reunion, but he's now engaged to the 'social climber' Veronica. Timeshare salesman Vince is none too pleased to see his old adversary Tony again, but it's the last straw for Vince when they both turn up to the fancy dress party night dressed as Batman. The happy hippy couple Pearl and Dean do their best to keep the peace ('man'), but it's no easy task.
Frankie and Duggs switch their plan and are now tunnelling through to the Bank from the Ladies' loos. Unfortunately this means they have to spend half their time in drag, wearing clothes they have purloined from Janet and Jane, who coincidentally take a shine to Frankie and Duggs. Confusion sets in when they think that the 'slappers' are rivals for their affections towards the tunnelling twosome.

Maria, the dissatisfied chamber-maid helps Vince to make trouble between Tony and Veronica, but it all backfires when Karen and Tony end up not speaking to one another, and then take out their aggression in the Men vs Women hockey match that the school has arranged
Janet and Jane visit the Ladies while Frankie and Duggs are locked in a cubicle working on their tunnel. The girls think that the occupants are the two 'slappers' they met before and hilariously misinterpret the conversation they overhear. Veronica though hears our desperately digging duo as they discuss the bank robbery, and quickly ditches Tony to team up with Vince as they plan to cheat Frankie and Duggs out of the loot. In the 'blacked out' tunnel the four of them all collide in the darkness and then start negotiating a very dodgy deal to split the takings.

Tony is now free to be led by his heart, and (with a little help from Pearl and Dean) falls happily into the arms of Karen. The action concludes with the four conspirators being discovered early the next morning, having woken the other guests with their loud arguing. It's quickly discovered that the loot is worthless anyway as it's all in pre-decimalisation notes that were stored in the bank for burning.
Is the ending a happy one ? Certainly. Frankie and Duggs are relieved to get out of the deal with the awful Veronica, Janet and Jane decide to reform the bungling burglars, Vince and Veronica plan their next money-making scheme, while Karen and Tony finally become a couple.