Decepticons Underground is a children's book with optional companion audio cassette. It was written by John Grant and illustrated by Glenn Stewart. It was published in 1988.
Nothing has been heard of the Decepticons for some time so Optimus Prime sends out patrols to find out what they are doing. Soon all of Nebulos has been searched except the Nebulos Triangle, an area of electronic interference. A patrol comprising Quickswitch, Scoop and Quickmix is sent to the area and, after encountering difficulties with navigation and a whirlpool, they uncover an underground Decepticon base. After a chase through the tunnels, Scoop manages to block off the base's surface exit and Quickmix finishes the job by coating the rocks with rapid-set concrete.
- This story was released as an audiobook.
- In this book and the following one, the Autobots are led by the Powermaster Optimus Prime.
- Other newer characters, such as the new Headmaster and double Targetmasters, were introduced.
- Among those depicted in the illustrations appear to be Hosehead as well as Grapple and Hoist, neither of whom is usually depicted amongst the Transformers on Nebulos.
- No Decepticons are named in the text but the illustrations feature Fangry, Horri-Bull and Squeezeplay.