Now, according to the legend, Adrina haunts the place because that's where her treasure is actually buried. I think that's boring. I think, instead, someone bound her ghost to the location, to guard something of mystical value within the graves: perhaps the graves are a regio entrance, or a non-hermetic initiation site, or... or... or... something.
I'm having a problem nailing down the "someone" and the "something". None of the ideas that come to mind sound very exciting. Please help me brainstorm?
(Additional information: the magi are just post-Gauntlet, wandering around the Thebes tribunal checking out the various mystical sites with an eye towards founding a covenant of their very own. They're actually coming to Skopelos to check out Agios Ioannis -- aka the Mamma Mia church, except there isn't a church there yet -- but they're going to trip over Sendoukia first.)
The graves are very well cut/engineered, so this could be an initiation site for some disciples of Heron. Can't see any immediate follow on from that though.
Also they are graves, so maybe a terram-based mystery cult has an initiation script which requires being buried in a tomb for a week/month/whatever, and Adrina dug them up while trying to bury her treasure
(after having heard from the locals of the scary tales, she though that it would keep them from wandering up and investigating, maybe she should have listened!)
The maga who was trying to initiate, failed (but still got a flaw from the ordeal) and in a rage killed her. As this is Thebes, her covenant should have a Patron, and said Patron could have assited in binding the ghost of Adrina (The patron of the covenant could be a Hades echo: Underwold and Terram aligned). Adrina now guards the place from further interlopers.
One concept I have often liked- the ghost is a faerie, there is no treasure, but they draw vitality from people searching for the treasure which doesn't exist that the ghost warns them away from...
Not sure how I feel about the maga in question being Hermetic. If it's a Hermetic mystery cult site, it's almost certainly the Guernicus Terrae cult out of Hedyosmos. (Patron being Minthe fits very, very well.) If my players choose to found a covenant there, Hedyosmos is not going to react well at ALL. Squatters on top of the mystery cult site? Potentially subverting the guardian ghost, or taking her as their covenant Patron? That's going to go over like a lead balloon with a Ford Pinto in it.
On the other hand, that ought to make for some fun stories...
There are lots of ways to go even deeper now. Adrina tried to loot the tombs while an initiation was happening, and was bound there as punishment. Her new job is now to defend the graves to prevent any further disruptions of their rituals, which have LONG since stopped if the mystery cult is pre-Hermetic. Everyone thinks Adrina's treasure is buried there, so people keep coming to disturb her. If you do destroy Adrina, you can guarantee the stories will make a faerie-ghost appear and take over her role to propagate it, which can turn the site into a source of renewable faerie vis as you dig up a completely new 'treasure' each year. After some amount of time doing this, someone or other is going to raid the tombs enough to actually disturb the people sleeping there (and the previous mystery cult is no longer around to soothe them), so you're going to have a ghost war on your hands -
Okay, I may have gone to deep here.
one of the fun parts of Mystery Cults is they tend to like their secrets, which means that the mystery cult won't really want to step up and argue that the site should not be claimed - they have to find some way to do it without alerting everyone that its their sacred site. Or perhaps they want to let the players put up a covenant side (Maybe Adrina was stopping the cult form performing their rituals?) and as part of the requirement to found the covenant, an elder of the cult wants to move in to the site to 'study' the ruins, and he can police them and perhaps induct one or two players to the cult secretly. And if that elder happens to be a Tytalus, you can bet Gigas is going to start going into it -
Okay, I may have gone to deep here.
Perhaps her treasure was stolen years ago. The ghost is now obsessed with the treasure that isn't there. However, she is a faerie ghost. She poses as a ghost who will be laid to rest if only someone re-unites her with her/a treasure. Instead, she is actually fae--she regains vitality through enacting the "lay the ghost to rest by completing their unfinished business" trope.
*editted because I just realized I stole Silveroak's idea without having paid attention. Sorry!
Continuing the idea of the Mystery Cult, what would be the Mystery that the initiate is trying to learn? If you are willing to be buried in a tomb for a month, what supernatural power do you hope to gain? I'm curious what necromantic Mysteries people come up with....
Easiest would be to come up with a list of Virtues that could be granted, geared specifically towards this theme. (Much easier than inventing a new Supernatural Ability):
Minor Magical Focus in Ghosts
Major Magical Focus in Necromancy
Dowsing, but instead of water, it leads you to the nearest corpse that was not given Christian Burial.
Inoffensive to ghosts (if a Gifted character without Gentle Gift)
Keen Vision (a bit lame, but you were underground, after all)
Second Sight
Ghostly Warder (An unquiet dead bonds with the character)
Death Prophecy (spirits whisper exactly how the character will die)
Special Circumstances (while underground)