Spark Unlimited has a goal of making their FPS Legendary look like a disaster movie. Judging by the chaos and destruction Thundrbolt was shown on the first level alone, they definitely succeeded. Things start off when Deckard, a professional thief, breaks into a museum to steal an artifact for an anonymous client. He inadvertently opens Pandora's Box and the whole "disaster movie" vibe comes into play.
He runs through the museum as everything around him is getting obliterated. Columns crash down and the ceiling is ripped apart by some mystical force. People were screaming and running for their life to escape the museum.