The Frozen Telescope by Jennifer Bell

After the thrilling events which concluded The Smoking Hourglass, Ivy, Seb and Valian think they've vanquished their enemies, and those of Lundinor, forever. It turns out their adventure was only just beginning . . . 

Ivy and Seb can't wait to join Valian for their first ever overseas uncommon adventure - they're meeting in Nubrook, the completely astonishing and totally-different-to-Ludinor trading market hidden underneath New York. But there's no time to enjoy looking round all the incredible sights - they're on a mission to find Valian's long-lost sister, Rosie.

But it seems they're not the only ones looking for her. Once again the Dirge rear their terrifying heads, and it appears they're after not only Rosie, but another enormously powerful Great Uncommon Good object. But what do they want it for? And can Ivy, Seb and Valian stop them from finding it?