One False Step by Franklin W. Dixon

a feeling it’s all connected to some of the acrobats in Aérocirque,” Frank said.
    â€œMaybe it’s not just some of them, Frank,” Joe said. “It could be all of them.”
    â€œI think I agree with Joe, Frank,” Mario said.
    â€œThat would be a major crime operation, but I guess it would make sense, given that each night there’s a troupe of acrobats that don’t perform,” Frank said.
    â€œWell, we know now that we were right about what made all those scratches on the balconies,”Joe said. “That grappling hook and that rope are pretty much a dead giveaway.”
    Mario nodded. “The evidence technicians will check everything out,” he said, “but I doubt if there’s anything here that will tie Aérocirque to the robberies.”
    â€œWhile we’re waiting for them, let me tell you about another one of my theories,” Frank said. He pointed to the apartment building across the street. “I think that somehow the thieves shoot the rope from the top of an apartment building across the street and tightrope walk to the empty apartment.”
    â€œThat’s a little far-fetched, isn’t it, Frank?” Mario said. “Wouldn’t people see them?”
    â€œThink about it, Mario. Who goes around looking up in the sky all the time?” Frank said. “People are so busy hurrying to wherever it is they’re going that they seldom look around , much less up . Anyway, the thieves do it at night. That makes it less likely they’ll be seen.”
    â€œFrank’s theory makes a lot of sense, Mario,” Joe said.
    â€œWell, I guess that means you still believe they reached the top of the other apartment building by helicopter,” Mario said.
    â€œMaybe not the apartment building itself, but a building nearby,” Frank said. “Just look around you. There are helicopters flying all over the nightskies of Philadelphia. Police. Radio and television personnel. Doctors. People don’t pay attention anymore.”
    â€œIf they happen to hear a helicopter that’s a little louder than usual, they probably just think something’s going on nearby,” Joe added. “Unfortunately, people don’t want to get involved in anything that doesn’t immediately concern them anymore, so they ignore it.”
    â€œWhy don’t they land on top of the apartment building?” Mario asked.
    â€œMaybe they don’t want to take a chance on the one person in the apartment building who would get curious about the noise,” Frank said. “They land on office buildings, where there are fewer people around at night.”
    Just then some midtown detectives arrived, along with the evidence technicians.
    Frank and Joe followed Mario back into the living room. “It’s all yours, guys. I can almost assure you that you won’t find anything inside the apartment,” Mario said, “but there’s a grappling hook and a rope attached to it out on the balcony, which I want to see if you can connect to Aérocirque.”
    â€œThat flying circus that’s in town?” one of the evidence technicians said. “You’re kidding me.”
    â€œNo, I’m not,” Mario said. “Come on, boys,” he said to Frank and Joe. “We have some plans to make.”
    When they reached the lobby they passed the owner of the apartment, who was demanding that the police let him and his wife in immediately.
    â€œIt won’t be long, sir,” one of the officers was saying. “It’s important that we look for evidence to help solve this crime spree.”
    The front doors closed on Frank and Joe before they could hear what the apartment owner said.
    After they climbed back into the van and started heading out of downtown Philadelphia toward Mario’s house, he said, “I have an idea. It could be dangerous, but my officers and I will be with you all the way, and