Sir Malik explains they were working with the wizard Benele when the zombies attacked. They lost track of her and now the cultists are desecrating the dead, which is considered an affront to Tu'whacca. Offer to help and he'll explain that the cultists raise the dead soldiers to zombies.
Using this sacred emblem, one can sanctify the corpses and that will prevent them to be raised as undead. He gives it to the Vestige. Now go to the ruins at Merovec's Folly.
Search the ruins for five dead soldiers and use the emblem to sanctify the corpses. When all are done return to Sir Malik, now at Lion Guard Redoubt.
Find Sir Malik to let him know the task is done. He is relieved the Vestige has completed his business.