From the front of the book:

The Tower of Maraj is an adventure designed for five 1st-level player characters (PCs), and is part of the D&D Delve Night kit. Please review the instructions for use of the D&D Delve Night kit before using this adventure. The adventure takes place in the tower of a dead elf wizard, which has been taken over by raiders and bandits before its contents can be claimed by the wizard’s son.