Creation Character RPG Dragons and Dungeons Daishains The Sage says...
The main thing you would be aware of is that the Cult of Dragonkind, a group known for its worship of Tiamat and creation of dracoliches, has been causing a lot of trouble lately. Raiding settlements, mostly to steal people and valuable things for unknown purposes.
What isn't well known is that a great deal of wealth is being ferried from across Faerun to a single location. Castle Skyreach, a flying fortress stolen from the enigmatic Cloud Giants, and the party's current location, is a vital link in this supply line.
The basic idea here is that clever divination work in pinpointing the location of whatever you are after led you to this place. It being in the air and on the move, you used the teleportation network to get ahead of it and on gryphonback to intercept.
As to your particular macguffin, they wouldn't have bothered taking a saint's finger bone or things of that nature. As a suggestion, it could be a minor magical artifact of Lathander, one connected to a church that may have asked him for assistance in retrieving it.