Can You Hold Back The Dead?

Hold Back The Dead is a new free adventure available on D&D Beyond designed to highlight new monsters featured in the new version of the Monster Manual. The adventure is designed for four six level 4 characters, just like Scions of Elemental Evil and Uni and the Hunt for the Lost Horn. Also like those adventures the premade characters included in this adventure are Niko and the cast of the classic D&D cartoon. 

Hold Back The Dead is set in the Forgotten Realms and involves the mechanizations of one of the greatest threats to the Realms, the vile lich lord of Thay, Szass Tam. The characters are are tasked by the Lords Alliance to help guard Ironspine Keep, a fortress being repaired in order to watch over the Western Heartlands. Unfortunately for the goodly folks, Szass Tam can't allow this to happen and sends an army, lead by a spectral warlord, to take care of the mortals.

Meant to be played in a three or four our session, the adventure is broken down into four parts: First Wave, Second Wave, Siege Weapon Sabotage, and the Warlord. The adventure is pretty straight forward. The characters must fight off undead, handle and infiltration, and take out a wraith. It's all a simple, but solid piece. The adventure can help move a campaign forward too. Why does Szass Tam want the keep? Do the players use the Keep as a base of operations (turning it into a bastion)?