Peter and the Shadow Thieves by Dave Barry and Ridley Pearson

The book starts three months after the end of Peter and the Starcatchers.^[3] Slank returns to the island with more of the Others, including a certain Lord Ombra, to reclaim the trunk of starstuff lost in the previous book. When they learn that the Starcatchers have taken the trunk back to England, they set sail for London. Peter follows, fearing for Molly's safety, and with Tinker Bell's help conceals himself on their ship.

Once in London, Peter does not know where to find Molly. After unpleasant encounters with beggars, traders and the police, Peter finally gets directions from J. M. Barrie to Lord Aster's house, and rescues Molly from Lord Ombra in the nick of time. However, Louise Aster -Molly's mother- has been kidnapped by the Others, and the children must find Lord Aster who is guarding the starstuff.

Meanwhile, back on the island, the pirates are hunting the Lost Boys. They capture the boys to use as bait for Peter, not knowing he is not on the island. (from: http://en.wikipedia.org/wiki/Peter_and_the_Shadow_Thieves)

I Liked the first book more, but, I really did enjoy this story also. I will be reading the third book in the series soon!