A deaf girl named Alicia is on her way to Las Vegas with her cousin Sally. While at a gas station, she reads the lips of a man in a phone booth, who is discussing blowing up a casino. Alicia nearly runs Joe and Frank off the road while she and Sally head to the casino to try to tell the casino owner what they found out. Eventually, the Hardy Boys agree to help the two women. but now the man and his accomplice know who Alicia is and seek to stop her
—charmardee-smith