The achingly beautiful adventure series continues! Following Wren, Septimus, and Ramkin's escape on the ship The Nominal Charge, they find themselves pursued by Mercantile warships. Brought before the Chairman of the Guild, he offers to help Wren in her quest to find the Key that will restart the dying sun if they undertake a mission for him, one that will take them into The Deeps of the gaseous world Hot Air!