In a past entry I mentioned the book Follow That Hippo! This book makes direct mention of the hyenas, meaning The Outlands are most likely involved too.
In that post there was no cover image available, but now there is:
The cover doesn't tell us much, as it's just a group shot of The Lion Guard.
However the other book covers give us a sense of the story:
It's also possible that the cover is not final and subject to change like Bunga the Wise. It wouldn't matter much if it did or not, as it's an eye catching cover, and will make kids want to buy it when they see their Lion Guard pals on it.