The Vessel of Stars

From the publisher's website: The Vessel of Stars is a Dungeon & Dragons adventure suitable for four 4th-level player characters. Player characters find themselves escorting a child monarch to a mysterious location in an area stalked by extraplanar horrors, alien assassins, and secret forces. Two unallied group seek the queen. One wishes to kill her. The other wants to capture her alive. The players characters are her only defense.