"Snakes!" The place is alive with them. They're dropping from that tree!" While Betty and Wilma Worth run for safety, Kay goes to investigate the weird attack, which she finds has not happened by accident, but has been planned by a thief after their pocketbooks.

Kay, though alert to danger, finds herself each day more deeply involved in a strange mystery. It leads her finally to the Moleson Mansion, where the "murmuring portrait" of a gypsy hangs. Suddenly the picture vanishes, then reappears. Why? And where is the sinister-looking person who poses for it? Is the missing Moleson heir the same person?

How to untangle a seemingly hopeless riddle takes all the uncanny insight of Kay's sleuthing ability, as she endeavors to prove the identity of a odd character, and to protect a fabulous treasure sought by a crafty gang of thieves.