The Mystery of the Masked Rider by Carolyn Keene

“Well, I’d better get back to work.”
    â€œMe, too. Maybe I’ll catch you in your next class.” Nancy waved, and Marisa disappeared into Mr. Sunshine’s stall.
    On the way to the truck Nancy thought about the San Marcoses. Diego was a strict taskmaster, but Marisa was also very ambitious. For them, showing was big business, with high stakes. And now Marisa had said she was riding in the Worthington Cup, which meant she’d be competing against Colleen after all. Now the San Marcoses had a very good reason for wanting Nightingale out of the picture. The red and black mask might be just the evidence Nancy needed toprove that Diego or Marisa had thrown the nails into Nightingale’s stall.
    When she reached the truck, Nancy hurriedly unlocked the door of the truck cap and pulled out half a bag of grain. She didn’t want to leave Bess alone with Nightingale any longer than necessary.
    Half an hour later Phil and Colleen had relieved Nancy and Bess of their duties. Nancy had shared her information about the San Marcoses with Bess, but not with Colleen. She didn’t want Phil to know what she’d discovered.
    â€œI need to exercise Nightingale in the warm-up ring,” Colleen said. “Why don’t you two grab an early dinner? It may be your last chance.”
    â€œAre you sure you’ll be okay?” Nancy asked.
    Colleen gave her a reassuring smile. “Phil will be here, don’t worry.”
    â€œThat’s what I’m worried about,” Nancy muttered to herself as she and Bess headed down the aisle.
    â€œWhat are you mumbling about?” Bess asked.
    â€œI don’t like leaving Colleen and Nightingale alone with Phil.”
    Bess stopped in her tracks. “Do you still think he’s guilty?”
    â€œPhil is one of my main suspects.”
    â€œAfter all you found out about the San Marcoses? I mean, even though they were in Florida the night Colleen found Nightingaleloose in the barn, they could have hired someone to steal her.”
    â€œDon’t worry. Diego and Marisa are high on my list, too.” Nancy pointed to a wide door through which a stream of people and horses was moving in and out. “That must be the entrance to the arena.”
    â€œThis place is huge,” Bess said as they walked through the doorway and out into an open area, filled with riders exercising their horses. The floor had been covered with tanbark. Several jumps had been set up along one side. A walkway bordered the other side. The only thing separating pedestrians from horses was a rope strung between a row of wooden poles.
    â€œThis must be where Colleen’s going to warm up Nightingale,” Nancy said. “And look, there’s the entrance into the show ring.” She pointed to a high, solid gate that was just being opened to let out a horse and rider.
    â€œOur next contestant is Elsa Van den Berg, aboard Stowaway,” the loudspeaker system blared into the warm-up area and across the whole arena. Nancy watched as a rider in hunt clothes jogged a sleek gray horse into the ring.
    â€œI wonder where the food is?” Bess mused as they headed down the walkway.
    In front of them Nancy could see the entrance to a double stairway. “Over there, I bet,” she said, leading the way.
    At the top of the stairs the girls stepped into a crowded walkway the width of a city street. Concession stands and booths lined both sides. The booths were selling everything from artwork to horse feed.
    â€œThis is the concourse Colleen was telling me about,” Nancy said. “It circles the arena.”
    Bess’s eyes bugged out. “You mean there are booths around this entire arena?”
    Nancy laughed. “Yup. A hundred and twenty of them.”
    â€œOh!” Bess clasped her hands. “I’ve died and gone to heaven.” Immediately she set off toward a display of silver jewelry. Nancy grabbed her arm.
    â€œLet’s