The Hemlen Wisps

In life, the wisps were loyalists to the Republic of Merak. Their transformation into wisps and their ongoing suffering has completely corrupted all but one of them, Darena. The other three wisps, Herjen, Eliska, and Robern, have forgotten who they were and exist now as hungry undead.
If the PCs approach the area, Darena will maximize her light and call out to them in common. She will warn them against crossing the barrier, saying that her family will consume their life. The other wisps will start attacking her but will be unable to do any damage. They will also try to talk the PCs into crossing the barrier, insisting that there is treasure in the ruins. This is true: in addition to 250 gp in scattered coins, gems and jewelry, the broken statue hides a bag of holding containing more treasure.
If the PCs talk to Darena she will tell them what happened: long ago, her ancestor Errena Hemlen was instrumental in defeating the traitor Elcera Molend, saving the Republic of Merak from disaster. For her service, Errena was given a magic sword, magic armor, and land (including this land). She was praised as being among “the bright stars of loyal soldiers.” Molend’s family was stripped of their land (some of which was given to Errena) and wealth, although the innocent family members were allowed to remain free.   The Hemlen family thought of all this as ancient history until Merak was plunged into chaos. The wizard Trenol, a descendant of the Molend family, was driven to take revenge against the Hemlens, deciding that transforming them into will-o-wisps would be a way to mock the praise given to Errena about being a bright star. Darena will say that Trenol was once a well-respected wizard who had restored the family name, but the madness of that time consumed many a soul. Darena, once a cleric, believes that she and her family can be freed if the curse is removed from their skulls (which are fused to the barrier stones). If she thinks the PCs will break the curse, she will ally with them to help defeat (and thus free) her family.
If the PCs cross the barrier, the three other wisps will attack them and try to consume their life. Darena will try to dissuade them but will be able to do nothing. If the PCs attack Darena, she will fight back. The wisps will make use of their invisibility to attack with advantage and, if the fight is going badly, to try to hide from the PCs. If the PCs flee, the wisps will probably not be able to pursue. They can return later and try again. If the PCs kill the wisps, they will reform the next dusk. This can be prevented by either destroying the barrier stones and the skulls or casting remove curse on a skull. Destroying the skull prevents the wisp from reforming, remove curse frees the soul from the curse, allowing it to go on to the afterlife it earned while alive if the wisp is killed.
If the PCs remove the curse from her family and agree to do the same for her, Darena will tell them about the bag of holding in the statue and explain how to open it without triggering the trap.
The statue, which is of Errena, has a secret compartment hidden behind the breastplate. The compartment is trapped so that if it is not opened properly, a blade will slice the bag of holding, scattering its contents into the astral plane. Spotting the trap by examining the breastplate requires a successful DC 15 Wisdom (Perception) check and disabling it requires a DC 15 Dexterity (Thieves’ Tool) check.
Within the compartment is a bag of holding. The bag holds a bundle of legal and financial documents, including the deeds to Thunderfall Hideaway in the city. There are also 10 100 gp gems, 50 pp, a 250 gp ring, and a suit of adamantine chainmail armor.
While Darena hates existing as a wisp, the PCs might be able to convince her to assist them in their mission. Darena is proud of her family’s loyalty to Merak and she would be susceptible to appeals to that loyalty, such as focusing on how a strong Rel could be the foundation for restoring the Republic.