It's Friday night, and teenage girls are full of excitement as they rimp for a dance at the local Holiday Inn. But for this group of girls in Sioux Falls, S.D., the night's dream date is not a teenage boy.

"I'm going with my dad instead of a boyfriend," explains 15-year-old Angela Merkle.

She and her two sisters are about to be escorted by their father to what's called a Purity Ball.

The event shares all the hallmarks of a wedding: Vows are exchanged, a white cake is served and there is even a first dance. But at the beginning of the event instead of fathers giving away their daughters' hand, they're holding on tight.

The event's purpose is to celebrate father-daughter bonding, but the main focus of the evening is for the fathers and daughters to exchange pledges in an elaborate ceremony. Fathers vow to protect the girls' chastity until they marry, and the daughters promise to remain abstinent.