Passage to Dawn by R.A. Salvatore

In the fourth and final book of the Legacy of the Drow series, it's been six years since the battle for Mithril Hall took place in the dark caverns and it's been six years since Drizzt and Cattie-brie have been back. However, when their friend, Captain Deudermont, is attacked by a doppelgänger, Drizzt and Cattie-brie are inevitably lured off their ship and back to Icewind Dale where an evil awaits.