The Tomb of Raven Darkmore

From publisher blurb:

Raven Darkmore is the legendary Grandfather of Assassins. He has ruled the night for the last forty years. Now he has been laid to rest. The location of his tomb has been a mystery until recently. A pair of thieves have found the location. Unfortunately, one of them died, trying to explore the tomb. His partner decided that he needed a little help. He has contacted the party offering to lead them to the tomb for a share in the treasure.

But not everything is as it appears. The thief leading the party to this tomb is not trustworthy. And the tomb is not as empty as it might seem.