VI's grandfather dies, and leaves her and her rather annoying cousin an estate in northern Tyrolia, among the Alps and near the German border. Brad, Noelle, Martin, and VI leave to investigate. (We rapidly associate Martin with Fred, VI with Daphne, Brad with Shaggy, and Noelle with Velma. Slade, when he appears later, becomes Scooby.)
It becomes obvious a lot of paranormals are interested in this mansion: agents of the Italian government (evidently Technocracy), members of the Mafia (Giuseppe Pedanno, a Glass Walker), a mage from Doissetep (Avis Malone), Nordic crewcut superhumans (assumed to be werewolves, probably Get), a Tremere vampire (rapidly offed by the Get), and another set of vampires with power over ghosts all make their appearance and make various threats, cajoles, power plays, and outright assaults to try to take this mansion.
Investigating why this place should be so important, they find a secret door in the back that leads down to an abandoned old Nazi war room. At the back of this war room is a fireplace, with another secret panel that leads down to an ancient tomb, a burial place for a lot of apparently Roman legionnaires and a fifty-foot-tall giant, with a worn panel at one end that says "APES".
It takes a while to realize these symbols are Greek, and that the P is a rho. About this time they call Slade, and he arrives vulgarly with help from (either the Sons of Ether or werewolves).
They scavenge a bit, taking a rusty sword and a finger bone [and maybe some other things?]. After some additional (partly magickal) detective work, it's determined that the energies pouring from this tomb of the God of War may have been responsible for setting off World War II, and that some of the factions outside appear to want to control and harness this power for themselves...
The Technocracy unfortunately appears to have the most reasonable idea: seal the tomb off and spin it out into the Umbra. The Glass Walkers kind of support this as well. All the other factions are pissed to some degree. Slade and Martin accidentally time-travel back to when the fireplace was lit, and talk to VI's "grandfather", who appears to have been a faerie or spirit or some Umbral creature, whom they help return to his home -- thus putting out the fire in the fireplace that originally served to seal off the tomb. They light a stick from this fireplace and return to the present, unfortunately disturbing (before the fact) dust that hadn't been disturbed for centuries, and taking a hit of several Paradox as a result.
The fire is relighted and the tomb of Ares becomes inaccessible again.