The cover by Rebekah Isaacs shows Xander and Dawn mingling with demons, no worries. But if they have gotten trapped in that hell dimension that appeared in #24 (the one opened by the Restless Door), it's a place as bad as Connor's Quor'toth! How Xander and Dawn alone will take all this, how they will survive?
And Dawn, The Key, isn't being able of open it back the Earth - would it be because The Key only opens portals from Earth to other dimensions? It was "an ancient mystical green energy with the power to unlock the gates between all existing dimensions", but it was from our dimension and maybe it doesn't work in others? Or the rules written on the book are making it difficult for Dawn to open a portal to Earth - and then, Buffy will write something on it to save her sister.