Neil Gaiman & Michael Reaves - Interworld

Joey Harker is an average high school student living in Greenville. He has trouble finding his way around his own house, let alone the town. On a field trip set by his Social Studies teacher, Mr. Dimas, Joey finds himself lost in the city. He then enters a strange fog and when he emerges, everything has changed. All the cars are brightly coloured, the police cars flashing green and yellow, instead of blue and red. He goes back home and discovers that he does not exist anymore, instead a girl named Josephine lives there. He runs outside and bumps into a man wearing a mirrored mask called Jay. Before Jay can explain anything, three men, standing on floating silver disks and wearing grey outfits, are trying to catch Joey using silver nets. Joey runs, unintentionally entering the fog again.

Afraid of going back to a home where he doesn't exist, Joey decides to go to Mr. Dimas for help. Mr. Dimas is shocked to see Joey, telling him that he had drowned last year and that Mr. Dimas himself had pulled Joey's body out of the river. Suddenly a woman appears in the room bewitching Joey into following her. She calls herself Lady Indigo and is joined by two other men. One, called Scarabus, has mystical tattoos all over his body. The other, a man with transparent skin, is called Neville. They move Joey to a flying ship, the Lacrimae Mundi.

The ship teleports to Nowhere-at-all, a sort of hyperspace. They are heading towards a place called HEX Prime. Before they can reach there Jay arrives and helps Joey escape, getting injured in the process. Joey opens a portal to the In-Between, a multidimensional world, where only Walkers and MDLF (multidimensional life forms, or mudluffs) beings can enter. The in-between is a shortcut for traveling from world to world. Joey and Jay exit in-between and arrive at a desert. There Jay explains to Joey how he is part of an organization called InterWorld and their job is to keep the altiverse balanced by stopping the scientific force (Binary) from making worlds too scientific, while also stopping the magical force (HEX) from making worlds too magical. Jay also says that Joey has the ability to "Walk", or go into the In-Between and other dimensions quickly and effectively.

A mudluff which looks like a bubble and communicates using colours appears. It seems to be trapped somewhere, Joey approaches it, As Joey tries to free the mudluff, a giant serpent (Revealed in the second book to be called a Gyradon) appears, biting Jay. The mudluff kills the serpent but Jay is already dying. Before he dies he gives Joey the direction to Base Town, where InterWorld HQ is. With his dying breath, he shows Joey a mathematical equation that will lead to Base Town: {IW}:=Ω/∞ (InterWorld is Omega over infinity). The mudluff becomes attached to Joey after he saved it, and Joey names it "Hue". Joey goes to HQ and learns that all Walkers are all copies of himself from different Earths. He begins an intense course of exercise while studying very advanced science and magic to prepare him for his new role as a member of the InterWorld. Many of the other Joeys initially resent Joey for causing Jay's death, but soon come around about him as his skills improve.

After a few months, Joey and four other Walkers go on a training mission. They are supposed to retrieve some signal beacons in a more scientific earth. But the earth they go to turns out to be a "shadow realm" and is in fact a trap, set by the same people who captured him earlier. Everyone in the team is captured by HEX, except Joey who is saved by Hue. When Joey escapes back to HQ, the leader, an old man named Joe, decides that Joey is not capable of working in InterWorld, and wipes Joey's mind of his life in InterWorld. Joey is then returned home, where he thinks nothing has happened, but feels like something's missing. After some time, while blowing bubbles with his little brother, Joey remembers Hue, and every memory about the Altiverse comes back to him. With all those memories back, Joey says goodbye to his family, Walks into the Altiverse again, and sets off to save his teammates.

With Jay's words in his head and Hue's help, Joey finds the airship where his teammates are being held, and lands safely on it. However, he is captured as well and taken to meet Lord Dogknife, a large hideous goblin who leads the people who captured his teammates. Joey is then taken to the room where his teammates are being held. A large cauldron is in the center of the room, built to capture their souls to power the ship. The HEX boil down Walkers to their raw essence, which is used as power supplies for their transdimensional spacecraft.

Joey manages to move over to the cauldron and knock it over, incinerating some of the guards in the room. He then moves over to untie his friends, who all try to find an exit so they can go to the engine room and shut the ship down. They find an exit and escape to the engine room.

The engine room is filled with souls from other Walkers, powering the ship. Joey and his teammates break the jars containing them to shut the ship down. The engine explodes, and Joey and his teammates plan an escape from the Nowhere-At-All. They talk of a gate in the Nowhere-At-All from which they can escape, but it is closing quickly. Joey decides he will not leave without Hue, because it has saved his life multiple times.

Many soldiers come into the destroyed engine room in an attempt to recapture Joey and his teammates and then Scarabus appears to fight them. J/O, a cyborg Joey, steps up and defeated Scarabus, and everyone goes to find Lord Dogknife.

Dogknife is in the room where Joey saw him earlier, captured by the souls and thus rendered harmless. Joey finds Hue and escapes with his teammates. They are about to escape when Lady Indigo appears to face them. Joey distracts her from fighting them with some powder in his pocket, and Joey and his teammates escape through the gate when he remembers the mathematical equation that will take him home: {IW}:=Ω/∞.

They return to the Old Man, who does not congratulate them for their heroic work. Instead, he lectures them on all their wrongdoings in the Altiverse. However, he now says Joey is allowed to stay without wiping his memory. The group sets out on their next mission.