Thianna and Karn's quest to retrieve the Horn of Osius takes them to Thica, where the two heroes try to overthrow the queens by beating them at their own game.

Byx is the youngest member of her dairne pack. Believed to possess remarkable abilities, her mythical doglike species has been hunted to near extinction in the war-torn kingdom of Nedarra. After her pack is hunted down and killed, Byx fears she may be the last of her species. The Endling. So Byx sets out to find safe haven, and to see if the legends of other hidden dairnes are true. Along the way, she meets new allies--animals and humans alike--who...

Newly arrived in 1892 New England, Abigail Rook becomes assistant to R.F. Jackaby, an investigator of the unexplained with the ability to see supernatural beings, and she helps him delve into a case of serial murder which, Jackaby is convinced, is due to a nonhuman creature.

"Endling: The First is the second book in an epic middle grade animal fantasy series by Katherine Applegate, Newbery Medal-winning and #1 New York Times bestselling author of The One and Only Ivan, Wishtree, and Crenshaw! To learn if she truly is the last dairne in the world--the endling--Byx and her friends must travel into the snow-covered mountains of the country of Dreyland, where they hope to uncover the truth behind the legend of a hidden dairne...

A trilogy conclusion finds Byx and her friends discovering that the same extinction facing the dairnes is threatening all living species, prompting the team to recruit creatures throughout the world into their revolution.