The Obelisk Trap — Margaret Pearce

When Billie, Charlie and their uncle are mysteriously transported to The Place of No Name, they find themselves in a land carved from nothing by The Traveller; lord and master of this strange world.
With no way home and strict rules to obey, the danger increases when they discover that girls and trouble makers are 'unloosed'-disintegrated, unbound, liberated, gone to God. Where they disappear to, nobody knows, but they are never seen again.
The newcomers have a deadly secret that must be kept at any cost. Billie is a girl
Escape is the only option they are interested in; and they need to do it fast. They don't know who they can trust. There are eyes and ears everywhere. And Billie can't seem to control her smart mouth. She's sure to get herself into strife one way or another.