Brains invents a green sludge that will make people invisible. Unfortunately Doughnut thinks it's food, eats it, and actually becomes invisible. He decides to have some fun.
Whilst autograph hunting at the gate of the local film studios, a glamorous star's dog escapes from her car. Chasing the dog leads the gang onto a war film set, a horror set and more.
On a visit to a stately home, Billie and Tiger get locked in the dungeons. Looking for them, everyone else gets separated and scared by the thought of the ghosts, especially Anne Boleyn's.
When in the countryside on a caravan holiday, the gang antagonize two posh campers, first by blocking their way on the lane, then when their donkey wrecks the couple's tent. Then there's a massive rain storm.
The gang discover a down and out musician sleeping on their bus, so help him by changing his image, name and musical style, turning him from Sidney into The Cool Cavalier. Now they need to promote him.
Brains creates a golf playing, dancing robot called Robbie for entry into a television show, though they use him to rescue Tiger's tiger from an angry man's garden who's already been pelted with Robbie's golf balls.
After having driven his go-kart on the road in a dangerous fashion, Spring is taken to court and charged with 6 motoring offenses. The gang as witnesses tell the Magistrate the story of how Spring came to that point.
The gang go and help Mrs Vickers before and during a visit by her evil landlord. Things as usual, don't go according to plan, so to help against her eviction, they do odd jobs to earn some money for her house repairs.
Whilst converting his black and white TV to colour, Brains and the gang receive a news report about an alien invasion from Planet 7. After decontaminating Doughnut they start fighting back, not realizing it's all a publicity stunt.
Tiger befriends Barney, a one-man band street musician. After constantly being moved on by a policeman, he hides out with the gang. After lots of fun and games, he leaves, and Tiger feels sad and takes it the hardest.
Albert is collecting silver foil to make money for a guide dog for the blind. As he needs 30 sacks, he and the gang put on a comedy sketch show called the Ha Ha Show with the audience paying in silver foil.
Local shop owner Mr Beaumont wants to turn the gang's den into a car park to service his shop. When the workmen arrive to start clearing the yard, it's up to the Double Deckers to stop them.
When Billie brings back Scratch the dog to look after for a week, for which she's being paid £2, the gang get the idea to create a Holiday Home for Pets to earn some cash. Step up Mr Furber and his flea circus.
When a hot new female teacher starts at school, the boys all fantasize about her, though Billie sees her as a witch. When a charity musical show she is organizing loses its rehearsal room, the boys offer up their place.
