"I know," admitted Cahill, grinning, "but O’Connor and me have worked out a plan. We figure that in the past these guys have been able to slip in between the detectives on watch. You see, it’s pretty dark in those woods at night. Our plan is going to put a stop to that. It’s like this: "We’re going to put a peg in the ground on each side of the tree, back and front. O’Connor will be on one side and me on the other. There’ll be a string from each peg running to O’Connor, and the same thing on the other side to me. We’ll hold these strings, one in each hand. Now, that completely surrounds the tree, so that anyone approaching will kick into a string. We’ll know from the hand the string’s in just what direction to look for them in the dark. O’Connor’s strings will be A and B, and mine will be C and D. Get the idea? "If O’Connor feels a tug, he’ll yell A or B at me. If I get a feel on one of my strings I’ll holler C or D. Get me? Then we’ll both make a rush at just the right spot. Believe me, Mr. Forrester, we got them this time. No sneaking up between detectives _next_ Saturday night." "The idea sounds very good, Cahill," agreed Forrester. "Perhaps it will work. If I don’t hear from you in the meantime, what hour do you wish me to approach the tree on Saturday night?" "We’ve fixed on ten-thirty, if that is convenient for you, Mr. Forrester," answered Cahill. "That suits me," declared Forrester. "And now, we’ll be going," announced Cahill, rising. "Thanks for the cigar. As fine a smoke as I’ve had in a long time." "Bang up," murmured O’Connor. "Take another along," suggested Forrester, accepting the hint. The two detectives each carefully selected another cigar, and then Forrester went with them to the door. "What will you do if the ghosts supposed to haunt that tree should appear?" inquired Forrester. "You don’t believe that stuff, do you, Mr. Forrester?" asked Cahill, scornfully. "Well, several people, unknown to one another, have agreed on the details." Cahill smiled. "Maybe so," he said, "but don’t forget that O’Connor and me can shoot, Mr. Forrester. We can lay out any ghost that ever ghosted." "You certainly have my best wishes for your success," said Forrester. "Don’t worry any more," assured Cahill, as he passed out. "The police have got this gang dead to rights _this_ time. Saturday night will end it!" CHAPTER XI—TELEPHONE CALLS "Son," said Mrs. Forrester at breakfast Friday morning, "Josephine and I have changed our minds." "About what?" prompted Forrester. "We are moving out to ’Woodmere’ late today instead of tomorrow morning. The Prentices are giving a dinner dance, the first of the summer season, Saturday evening. If we moved tomorrow we would be too tired and upset to attend. We do not want to disappoint the Prentices, especially as we understand the affair is given to introduce Miss Sturtevant." "Does she know the Prentices?" exclaimed Forrester.