A primordial evil threatens the Dreamlands, but there is hope: an ancient power known as "An Cupla" - the Twins - can defeat the threat and drive it back into the Great Abyss. And the Cats of Ulthar are convinced that two energetic and carefree young ladies from the Waking World are the current manifestation of that power.
Eile Chica and Sunny Hiver - known as Team Girl - share adventures as well as their lives, but when their pet Snowshoe Kitty and her family perform a magical ritual, they find themselves in the Dreamworld, held captive by the Cats who demand that they save it from this eldritch threat. If they refuse the Cats will kill them.
The mission itself sounds suicidal, but with no other choice they set off, accompanied by a curmudgeonly feline huntress named Shadow-Stalker as their guide. First they must steal an artifact that is critical to their success, which is being guarded by an alien monster. Then they must journey to a monument that can stop the threat, if they can figure out how to make it work. All while avoiding the villains determined to stop them.
None of their experiences in the Waking World have prepared Team Girl for this kind of adventure, and they cannot even be sure the Cats are right about them being the Twins. Even with the assistance of the legendary Gaelic warrior queen Medb hErenn, their chance of success is slim at best. But succeed they must, or a nightmare from out of the abyss of time will destroy both the Dreamlands and the Waking World.