A group of highly psionic worms lived on a planet near a dimensional nexus. Bianca's Cabaret was established on top of their planet, and various factions of those worms tried to use the nightclub's staff and clientele for their own ends.
The typical worm was a small creature, less than an inch long — certainly small enough to fit in a makeup compact. It was green, and offered no physical threat. The worms thrived on alcohol, either as their natural medium or as a food supply. If a patron of Bianca's were to ingest any of the cabaret's "house special" tequila, it would realign that person's psychic wavelengths in with that of the worms. The worms could then influence the person, and in many circumstances control them outright.
The worms occupied a small dimensional nexus, containing wormholes to many different times and places across the universe. The local conditions were a calm point amidst the chaos of inter-dimensional space. The worms perceived that the universe's influence would change their race into more complex beings with limbs and hair and other higher-structure elements... and were horrified. Most worms considered themselves already perfect.
The worms had differing ideas on how to deal with the situation, and split into opposing factions. The Pro faction wanted to take firm control of the entire universe, keeping all life in a static condition. The Anti faction wanted to cast the universe into total violence and chaos.
A third faction, the Shadows, were the evolved creatures that the worms would have been, given vague form as "potentials" by the physical properties of the nexus. They wanted to use the other two factions so that they could bring their full existence into reality. (AUDIO: The Wormery)
When Bianca crashed her TARDIS on the worms' planetoid, the Pro faction saw an opportunity. They worked with Bianca and her compatriot Henry to set up a trans-dimensional nightclub that would attract the most influential people in the universe. The worms planned to use Bianca's singing to project a universe-wide compulsion of unity and harmony.
The Anti faction, needing an avatar of their own, found Iris Wildthyme and directed her to Bianca's nightclub. Besides interfering with Bianca's plans, the faction planned to use Iris' singing to generate a universe-wide compulsion towards violence, sex, and other base desires.
The Shadows found an ally in Henry. Working behind the scenes to help both of the other factions build their psychic amplifier, the Shadows intended to physically possess all of the people in the universe, giving them the corporeal existence they desired.
Into this arrived the Sixth Doctor. He was quickly caught up in the machinations of all three groups. Seeing no other way of stopping the universal broadcast, the Doctor used his TARDIS to time ram the nightclub. The resulting explosion destroyed the club, leaving all three factions of the worms with no means of doing anything. (AUDIO: The Wormery)