The boy peered through the crack in the boarding, and again reported no one in sight.
"Come with me to the roof," said his uncle. "From there we can survey a wide extent of the park. Armstrong will oblige me by remaining on guard."
He led the way up the stairs to the topmost room. Here he opened a low door in the wall, which gave access to a short flight of steps leading to the flat roof. Looking out towards the river, they saw a group of men gathered about the well-head. A moment later they caught sight of Gradoff and the two strangers approaching the tower from the direction of the house. Mr. Pratt leant over the parapet in full view, watching them. One of the strangers noticed him, and caught Gradoff by the arm. The Russian looked up, halted, and seemed for a moment to be taken aback. The three men spoke rapidly together, then advanced to the foot of the tower. Gradoff tried the door. Retreating a few steps, he called up--
"Holà!"
"Well?" said Mr. Pratt, leaning on the parapet.
"Come down and open the door. I have a proposition to make."
"Make it now. I can hear you quite well."
"You have Olof Jensen in the tower?"
"He is a prisoner. Yes."
"I also have a prisoner--one of three boys. I exchange him for Jensen, on condition that you come out with the other two."