Jamal Walker (MARTIN LAWRENCE) is a 21st century man who, along with his buddy Steve (DARYL MITCHELL), works for Mrs. Bostick (ISABELL MONK) at Medieval World Family Fun Center. Not the most loyal employee, Jamal already has his application ready for Castle World, a competing attraction set to open in two weeks.
He doesn't get the chance to apply, however, for when he's cleaning out the moat and trying to reach a medallion he's spotted, he's pulled beneath the water and suddenly finds himself in 14th century England. Of course, he doesn't realize that, and instead thinks he's somehow stumbled over to Castle World and is impressed by what appears to be quite the level of detail they've applied to the setting.
After meeting former knight and now loner drunk Sir Knolte (TOM WILKINSON), Jamal enters the castle where he's mistaken as the messenger for the Duke of Normandy whose arrival is imminent. Jamal goes along with what he thinks is an elaborate production and meets what he thinks are various actors. Among them is King Leo (KEVIN CONWAY) and his daughter, Princess Regina (JEANNETTE WEEGAR), who has an eye for Jamal, as well as Percival (VINCENT REGAN), the king's no-nonsense right-hand man who doesn't like the foreigner he refers to as a Moor.
Then there's Victoria (MARSHA THOMASON), one of the King's chambermaids to whom Jamal is instantly attracted. She, however, is secretly working with others in a rebellion to overthrow the corrupt king and reinstate the Queen (HELEN CAREY) back into power.
As Jamal finally realizes where he really is and tries to get used to life in the 14th century and its trappings, he must decide whether to return to the 21st century or help Victoria, Knolte and others take on the king and his men.