The Triple Hoax (1979)

Aunt Eloise invites Nancy, Bess, and George to New York to help a friend who has been swindled out of a sizable sum of money. There, the girls see a performance of a magicians' group who stun their audiences with clever sleight-of-hand tricks. Because the magicians temporarily remove people's wallets and handbags, Nancy feels the actors aren't above suspicion. Her hunch is borne out and a whirlwind chase ensues.