No one can point exactly to where Crossover lies, but some years back a man named Titus Braden discovered a hidden passageway deep within a mine. When Titus and his dog, Tiffy T, made their way through the passageway, they ended up high above a valley in another world, a world much like the world they came from but with surprising differences.

Titus and a few friends establish a camp in the valley below and begin to explore. At first the world seems open to them. To the west, over a range of hills, they come to a sea (The Variable Sea). To the north and around to the northeast the valley slopes down toward another, lower range of hills, some of which are unstable (The Shifting Hills). To the Southeast and curving around to the south is a high, barren ridge they name the Rim.

This is the full extent of where they are able to go. What they saw to the north during their early exploration is soon cut off by something they call the Black Billow. Before long, more barriers (The Baby Gates) show up. The main valley, the nearest hillside slopes, and a stretch of the coast along the Variable Sea are theirs to explore, but something or someone is limiting them to that.

The one exception is The Lower Valley, a fog-covered region below where Settlement Creek cuts through the northern hills and disappears over the Edge. This exception, however, only applies to ex-toy dogs, to Rangers and Rangers-in-training. Humans are incapable of making that descent.