Ladybird Books were a UK publisher of children's books, based out of Loughborough in Leicestershire. Even though their first books were published in the early 20th century, it wasn't until the 1950s when the books began to gain in popularity, having their heyday in the 60s and 70s. They were the staple of many a child's life in that period.
Decepticons Underground is the final book in the 1988 series of Transformers books and is also the final Transformers book ever published by Ladybird. It was written by John Grant and illustrated by Glenn Steward. There was also a "Tell-A-Tale" version that was released, that came with the book and a cassette tape, narrated by Peter Marinker.
The plot to this book is Concerned with a lack of Decepticon activity on Nebulos, Optimus Prime has Kup arrange a series of long-range patrols to ferret out the villains. As the reports come back in with no success, it becomes apparent that there is one area of the planet that has not been searched: a mysterious region known as the "Nebulos Triangle," where electronics systems malfunction, and Nebulans have vanished over the years. Convinced that the Decepticons are either there or off-planet entirely, Prime dispatches Quickswitch, Scoop and Quickmix to investigate.
When the trio of Autobots enters the Nebulos Triangle, they quickly lose control of their vehicle-mode steering and have to unsteadily continue on foot. They discover the ground to be metal underfoot, and they follow a stream to a massive lake of mercury. While the two Double Targetmasters have no option but to go around the lake, Quickswitch assumes his hovercraft form and heads out across it, only to wind up being sucked into a whirlpool.
Quickswitch lands in an underground cavern and explores it in his puma mode, which can see in the dark. Finding no way out that he can fit through, he converts to drill-tank mode and bores his way out...into a brightly-lit tunnel someone else had made before him! He stealthily creeps down the tunnel and finds that it leads into the Decepticons' secret base. He immediately turns to escape and report his discovery, but in so doing, he dislodges a rock that rolls away and knocks over some fuel containers. An intruder-alert klaxon blares a moment later, and Quickswitch races back up the tunnel, shooting out the lights as he goes.
He makes it out into daylight, and fortuitously Scoop and Quickmix are nearby. Scoop comes up with an idea: While the other two fire their weapons down the tunnel to keep the Decepticons at bay, Scoop uses his excavator mode to gather rocks. After collecting enough, he tells the other two to get away, then he pushes the stones into the tunnel, where they become an avalanche that drives the Decepticons back. Scoop pushes load after load in until the passage is firmly blocked. Quickmix adds to Scoop's plan by having Scoop shovel fine sand and the mineral Nebulite into his mixing drum, where they are mixed with water and cement to create a super-strong, rapid-set concrete. Quickmix pours this over the rocks, which have already begun to shake with the tunneling efforts of the Decepticons. The concrete fills all the gaps and hardens immediately. Quickmix is confident that that will hold their foes a long time, so the trio happily sets off for home.
Thanks to RetroRobotRadio for uploading the audio cassette and scans of the book. For the final book, it's interesting that the Decepticons are simply defeated and imprisoned by being buried, It's also great to see Quickswitch and the Double Targetmasters in Scoop and Quickmix taking center stage in this story.