Harpies

Jason Avery is an ex-cop now working as a museum security guard. Armed thieves break in intent on stealing a priceless obelisk that looks like a glowing crystal dinosaur egg that's stored within this vault-like stone structure that looks like someone merged a Tardis with the Stargate. The scientist/anthropologist/whatever behind the theft talks of the obelisk giving him the power to control harpies, demonic winged female monsters of classic mythology. Through a series of contrived events, the obelisk opens a time portal that Jason promptly falls into, crash landing over a thousand years in the past in a land threatened by evil harpies. Initially only concerned with getting home, Jason gets roped into having to save the villagers, all of whom proclaim him to be this great "harpy slayer" that prophecy says would one day come to save the kingdom.