Peter and the Starcatchers2 books in series
Peter and the Shadow Thieves Summary
On a difficult journey across the sea, he and Tink discover the dark and deadly slithering part-man/part-creature Lord Ombra, who is intent on recovering the missing starstuff - celestial dust that contains unimagined powers.
In London, Peter attempts to track down the indomitable Molly, hoping that together they can combat Ombra's determined forces. But London is not Mollusk Island; Peter is not the boy he used to be; and Lord Ombra - the Shadow Master - is unlike anything Peter, or the world, has ever seen.