While dashing through the airport, four siblings (aged 5 through 15) pass through the wrong gate and find themselves transported to a different place entirely:

OVERTWIXT
the in-between world that links
all the many realms of the cosmos

Even if they wanted to go back to their parents in the real world, that decision is taken out of their hands when the bridge home is destroyed behind them. They have no choice but to move forward and explore the nilands of Overtwixt, strange floating islands linked by countless bridges -- stone bridges and rope bridges and winding staircases and soaring arches, every kind of bridge imaginable, and more besides.

And towering above them all, the imposing fortress niland of Twixt itself... where the Vizier rules with an iron fist, turning bridge after bridge into rubble so the peoples of Overtwixt can never escape.

Confronted with this strange new world -- and the evil that threatens to destroy it -- the four siblings must answer the same question all new visitors to Overtwixt face:

Who will YOU choose to be?