While sick in bed with cancer, Lucien begins making journeys to a place in a parallel world that resembles Venice, Italy, and he becomes caught up in the political intrigues surrounding the Duchessa who rules the city.

At nearly fifteen years of age, Joey Harker learns that he is a Walker, able to travel between dimensions, and soon joins a team of different versions of himself, each from another dimension, to fight the evil forces striving to conquer all the worlds.

Aidan's new friend Antoinette is called to the Realm, but when she arrives to rescue Robby through his Glimpse-twin, the place is in turmoil and she must decide whether to stay loyal to the one true king or join the evil side.

While passing through the Arch in St. Louis, Missouri, a Chinese American teenager is transported to a parallel world where she is given a dangerous assignment.

Seventeen-year-old Sky joins Georgia and the other Stravagante, "who travel between worlds and do what is required, " when he leaves London for Giglia, a city similar to Renaissance Florence, and becomes involved in ancient feuds and palace intrigue.

After thirteen-year-old Tucker Feye's parents disappear, he suspects that the strange disks of shimmering air that he keeps seeing are somehow involved, and when he steps inside of one he is whisked on a time-twisting journey trailed by a shadowy sect of priests and haunted by ghostlike figures.

Fifteen-year-old Georgia, who loves horses as much as she hates her bullying stepbrother, buys a figurine of a winged horse and finds it has magical powers that transport her from present-day London to the sixteenth-century world of Talia where, in the city of Remora, similar to Sienna, Italy, she finds danger and intrigue as well as friendship and a chance to perfect her riding skills.

Tucker Feye and Lah Lia each hurtle through time, relating their stories in alternating viewpoints that converge at crucial moments.

Fourteen-year-old Jason Walker is transported to a strange world called Lyrian, where he joins Rachel, who was also drawn there from our world, and a few rebels, to piece together the Word that can destroy the malicious wizard emperor, Surroth.

Feeling inferior to her talented twin brother, teenaged Isabel is transported to a parallel world that resembles the Italian Renaissance city-state of Ravenna, where she tries to save the city from attack by the fierce Gate people.