“Probably it was the same tube you just took apart,” Eddie said. “When Teena and I were rowing out to Cedar Point this morning, we saw the two men coming down the bluff carrying something shiny. Later, looking back from Cedar Point, we saw them anchored over the sand bar. Probably over the same place we found the cylinder.” “It figures,” Mr. Evans, the FBI man said. “For the sake of argument, let’s say the two men are spies. Could be even more than two here at the college or working at Acme Aircraft.” “Spies!” Teena gasped in disbelief. “Maybe they’re both hiding at the shack,” Eddie said excitedly. “You’d better go arrest them!” “Not so fast,” Mr. Evans said. “Arresting them isn’t nearly so important as finding out where the remainder of the radioisotope is hidden. Getting hold of the rest of those missing blueprints also is much more important than arresting two men.” “In fact,” Mr. Jamison added, “arresting them too early might tip off the whole operation, and everyone would run for cover before we could pin anything down.” Just then Teena’s father came hurrying into the office. “Sorry I couldn’t get here sooner, Steve,” he said to Mr. Taylor, “but we were trying to locate another very important set of blueprints. More secret guidance-system parts. I absolutely can’t figure how those blueprints can keep disappearing, and—” Eddie’s father held out the rolled-up blueprints which had been inside the metal tube. “These wouldn’t happen to be the ones, would they, Tom?” he said. One glance, and Mr. Ross’s face took on an expression of mixed pleasure and amazement. “They certainly are!” he exclaimed. “But how—” The FBI man interrupted. He brought Teena’s father up to date on the story thus far. Mr. Ross looked over toward Teena and Eddie. As pleased as he seemed over the recovery of at least part of the missing blueprints, he appeared even more concerned over something else. “If I had had any idea that you two were getting mixed up in anything like this,” he said, “I’d have insisted that you stay home and play scrabble or checkers or something safe.” “We—we weren’t mixed up in anything, Mr. Ross,” Eddie said quickly. “At least, we sure didn’t know we were, and—” “I believe,” the FBI man cut in, “that we’d better get down to cases. We may not have much time to solve this problem. Let’s see what we have to go on thus far. Then we’ll try to plan our next move.” Eddie listened as Mr. Evans reviewed the situation point by point. Two men—the one called Simms and the other known as Roy Benton—were involved in stealing the blueprints and the radioisotope. Mr. Evans didn’t seem at all worried about capturing them when the time was ripe. On each of the last three Saturdays, including today, Eddie and Teena had seen them fishing, or pretending to be fishing, over the sand bar in Moon Bay.