Yesterday Scotty had seen watchers on the shore, presumably from Calvert's Favor. Apparently the watchers were there now. The boys had gone into shallow water, and their tanks had shown above the surface, drawing fire. It was the only reasonable explanation. Probably the night watchers had seen the pole handed up to Orvil, or had seen the faint light reflecting from their masks. What had happened to Orvil? One thing was certain. They couldn't stay on the bottom indefinitely. Rick consulted his wrist compass and closed his fingers on Scotty's shoulder. He led the way toward the mouth of the cove. Somewhere on the shore, he thought, the night gunmen were watching the line of bubbles. The boys' only hope of escaping detection had been to avoid drawing attention to themselves. Rick knew that was impossible with watchers on the shore. Watchers at four in the morning was one thing he hadn't expected. What had drawn them? Suddenly he knew. While he, Steve, and Scotty had examined the mansion through glasses from Orvil's boat, Merlin and company, or a single guard, had been watching them. They had drawn attention not only to Orvil, but to the time of day when the guards would need to be especially alert. Bubbles would attract the guards' attention, not only because they foamed on the surface, but because they would leave a glow of phosphorescence. How far would bubbles and glow be visible? He had a mental image of the watchers following the shoreline. They couldn't cross the creek or its mouth to where Steve's runabout was stowed, but they could shoot that far, if they could see the bubbles. The only way for Scotty and him to escape was to eliminate the bubble track. That meant not breathing. Not breathing was possible for a short time. During the interval, they could swim into the marsh grass and use it for cover. Rick's thoughts raced. He tried to recall the shoreline. There must be some promontory, some outcropping of grass, behind which they could hide. Perhaps the best way was simply to swim directly out from the creek mouth until distance hid the bubbles and darkness shrouded two black-covered heads. There was a problem, though. Scotty's air tank hadn't been used until now. Rick's had, during the initial search yesterday. He estimated quickly. Less air is used at shallow depths than at deeper depths. The water depth for most of the way was shallow enough so that tank time was essentially the same as swimming on the surface. He had had at least forty-five minutes of air to begin with, and it might be stretched to fifty minutes. He probably had used no more than forty minutes of air, total. But the remaining ten minutes would not take them out into really deep water in the river itself, and then back to shore. There was not enough air to take them to Steve's place.