Here's my plot (I'm thinking of making it into a fanfic)
It's set twenty years after the end of the original series. Doc is dead, and his house is now being occupied by his son, Jerome Crystal Jr. (we can call him Jerry, as a reference to Jerry Nelson). When he moved into Doc's house, Jerry boarded up the hole that leads to Fraggle Rock, cutting off the Fraggles' access to Outer Space (since the hole leading to Doc's home in the desert was blocked by a rockslide years before, so they don't know about Doc's death). However, a couple of years before the events of the movie, Uncle Traveling Matt (who had returned home to Fraggle Rock years before the hole was boarded up), desperate to explore again, ventures into the Gorgs' garden, and never returns or even sends a postcard.
One day, Gobo sees the Gorgs taking away Marjory the Trash Heap. Before she disappears, Marjory the Trash Heap warns Gobo that Matt is in danger. Thus, the five Fraggles embark on a journey into the world beyond the Gorgs' garden to find him. Along the way, they encounter another Gorg, who wants the throne of the universe from Pa. Eventually, the evil Gorg leads an army of other Gorgs back to the garden to take the throne, but the Fraggles help defeat them. Meanwhile, a fire in Outer Space threatens to destroy Fraggle Rock.