Free Danger Zone by Franklin W. Dixon

Tony said in awe.
    Just then a flash of light caught Joe's attention. At first he thought it was glare off one of the ship's metal disks. But when he aimed his binoculars at the source he realized he was wrong.
    It was another pair of binoculars, focused straight at him.
    "Uh - oh," he muttered.
    The whine of an outboard motor broke the peaceful silence. A powerboat was racing toward them from behind the yacht. Joe quickly stashed the binoculars under his seat and grabbed his fishing rod.
    The boat didn't slow down as it approached. Instead it aimed straight for the stern of the small motorboat.
    Tony's look said it all. "What is this dude trying to prove?"
    The powerboat began circling Joe and Tony's boat counterclockwise, once - twice. It picked up speed, making its circle tighter and tighter.
    In its wake Joe and Tony's boat pitched up and down violently. The fishing rods clattered to the deck.
    "We're going to capsize!" Tony shouted.
    "Hang on!" Joe shouted back, clinging to the side.
    "What does he want?" Tony's voice had become a terrified wail.
    As if in answer, the powerboat slowed down and sliced back toward the yacht.
    From its deck a man in a windbreaker leaned out with a megaphone.
    "Better stay away, kids," his voice blared. "Or next time we go through your boat!"

Chapter 12
    "See you later, honey," the man said, leaning in the driver's window of the station wagon.
    Frank stiffened at the sound of the voice. It was Muldoon, the guard who had stopped him and Joe the day before in the lobby of the Center for Experimental Research. He was saying goodbye to his wife. In his right hand was a small box wrapped in birthday gift paper.
    Frank ducked behind his car, pretending to check his tires. When he looked back up the station wagon was gone, and Muldoon was walking through the front door of the building.
    It wasn't going to be easy getting in past Muldoon.
    Frank left the car and began sauntering toward the back of the building. The center sat on a slope, at the bottom of which was a truck dock - and, Frank hoped, an entrance.
    Walking downhill, he kept the dark-tinted windows of the center's first floor in his peripheral vision. They were all lit by overhead fluorescents, except for one that was pitch-dark. He was surprised to hear a flurry of whispers drift out of the dark room's half-opened window. He considered turning and walking around the building the other way.
    Suddenly the lights in that office flickered on, and a chorus of "Happy Birthday" blasted out. Frank gave a glance and saw Muldoon, Todd Brewster, and a couple dozen others singing to an embarrassed-looking red-haired woman.
    If he was going to get inside, this would be the perfect time. He ran to the truck dock.
    There was a door there, a heavy steel door with no handle. Frank tried to pry the door open with his fingers, but it was obviously locked. The sliding truck doors were padlocked, too.
    Frank ran a few feet to his right and looked around the corner to the back of the building. A solid wall of glass and steel stretched across its entire length.
    He decided to try the front door. As long as Muldoon was in the party room, Frank might be able to bluff his way in.
    He had gone only a few steps when the steel door burst open. Thinking fast, he ducked behind a large white trailer that was parked at the dock.
    "I can't believe she didn't know!" came someone's voice.
    "She told me it was a total surprise." That voice was Muldoon's - and it was coming closer.
    Frank felt the trailer begin to rock. Startled, he backed away. Did they know he was there?
    From within the trailer a jumble of male voices was heard. He caught a few snatches: "Where's my shirt?" and "I knew they wouldn't get that oil stain out!" and "They really shrunk this thing!"
    Frank realized the truck was used as some sort of makeshift dressing room. Suddenly it was clear to him how he could get into the center.
    He waited for the men to leave, listening for the click of the metal door.