Barmy Jeffers and the Quasimodo walk by J.H. Brennan?
Barney "Barmy" Jeffers is an ordinary boy with an enthusiasm for roleplaying games. He has developed an unusual gait, called the "Quasimodo Walk" which he performs in order to irritate his younger sister. One day, while exploring an abandoned building, he performs the Walk on an impulse and accidentally falls through into an alternate reality.
In the other world, he meets the Reverend Lancelot Bong, a cleric from the Order of the Church Militant, who takes him in. Bong explains that reality is like a Moebius Strip and that Barmy fell through from one "side" to the other as a result of the Quasimodo Walk - monsters can pass through the "twist" between realities, and the Walk makes Barmy resemble a monster. Bong proposes an expedition to find an expert in reality warps, so that Barmy can get home to his own reality.
They gather together a party of adventurers (each of whom embodies a parodic representation of a D&D class). This is fairly easy, because in this reality adventuring into the monster-filled wilderness in search of treasure is a popular (if dangerous) career. In addition to Barmy and the Reverend Bong, their party consists of:
- Facecrusher - a female fighter, and the expedition's leader.
- The Amazing Presto, a wizard who trains Barmy in rudimentary magic.
- Ben, a friendly dwarf.
- Aspen, an attractive female fighter (probably a mystic, in D&D terms) with a strange stone-ball weapon no-one else can lift.
- Pendragon, a paladin who is largely ridiculed by the rest of the party.
- Rowan, a thief who is accompanied by an enormous dog named Eyenek.
The party rapidly discover that the specialist they seek has been captured by the villainous Baron Tanaka. When they infiltrate his castle, they discover that Lauren (Barmy's sister) has followed him to the alternate reality and become Tanaka's Court Wizard, by dint of impressing him with a battery-powered torch. She attempts to help the party, but they are captured anyway. Tanaka intends to execute them all, but Barmy uses a spell to summon an entity known as a "slith" which destroys the castle, and the party escape along with Lauren and the specialist who was imprisoned in Tanaka's castle.
In the end:
The specialist demonstrates that all that is needed to create a portable "twist" is to make a large enough Moebius strip from paper and hang it up so that they can Quasimodo Walk through it. Lauren and Barmy do this, and return home.