The party is hired by an old but very wealthy patron to act as guards within a subterranean property that has been in their family for generations.
They are to ensure that nothing within the property is damaged and repel any ne’er-do-wells that make their way in. The patron themselves makes their home in some of the deepest chambers of the structure but makes it very clear that they will be keeping an eye on the party in case they get any ideas of looting the place themselves.
After the second or third attack, the group realises that they have been hired to defend a loot-filled dungeon from adventuring parties. But does that mean their patron actually is malevolent?