Frances Hardinge Collection 2 Books Set (Twilight Robbery, Gullstruck Island):

Twilight Robbery:
The city at night is a dangerous place . . .Mosca Mye and Eponymous Clent are in trouble again. Escaping disaster by the skin of their teeth, they find refuge in Toll, the strange gateway town where visitors may neither enter nor leave without paying a price. By day, the city is well-mannered and orderly; by night, it's the haunt of rogues and villains. Wherever there's a plot, there's sure to be treachery, and wherever there's treachery, there's sure to be trouble and where there's trouble, Clent, Mosca and the web-footed apocalypse Saracen the goose can't be far behind.

Gullstruck Island:
In the village of the Hollow Beasts live two sisters. Arilou is a Lost - a child with the power to depart her body and mind-fly with the winds and Hathin is her helper. Together they hide a dangerous secret, until sinister events threaten to uncover it. With a blue-skinned hunter on their trail and a dreadlocked warrior beside them, they must escape, or risk everything. Can the fate of two children decide the future of Gullstruck Island?