Chavez looked up sharply. "Yes! An ideal phrase for it." Rick recognized the quotation from his school-work. _Macbeth_, Act II. Another of Shakespeare's phrases from the same work leaped into his mind. "Macbeth hath murdered sleep." Not Macbeth, but Marks. Rick knew he wouldn't sleep well that night, nor for many nights to come. Dagger of the mind! Well, it fitted. Watching the blank face of what had been, only hours before, a brilliant scientist, Rick could feel its deadly point himself. CHAPTER X Search for Strangers The good weather turned bad, and dark clouds hung low over the New Jersey coast. It was appropriate weather for the state of mind at Spindrift. With Marks a victim of the mysterious "dagger of the mind," only Dr. Morrison remained of the original team. The question, of course, was "Who next?" At Hartson Brant's urgent request, Steve Ames visited the island and a meeting of all staff was called in the big library. Rick and Scotty sat on a library table, while the scientists occupied the few library chairs. Steve Ames sat on Hartson Brant's desk and acted as chairman for the informal session. By mutual agreement, the girls had been excluded. Jan was nearly in a state of shock over what had happened to Marks. Not only was she fond of the crusty scientist, but she was fearful that the mysterious ailment would strike her father next. And Barby was rapidly catching the same fear. After all, new team members probably were not immune, and Hartson Brant, Julius Weiss, and Parnell Winston were deeply involved in the project. Steve called the meeting to order. "Hartson, you suggested that I come, which I was glad to do. Suppose you start by telling us what you had in mind." "Very well, Steve." The scientist's glance embraced his colleagues and the boys. "We have a problem that must be solved before we can continue with calm and objective minds on the project that faces us. The problem is simply, what is the ailment that has stricken three of us, and what is its cause?" Hartson Brant tamped tobacco into his pipe thoughtfully. "Let us see what we know. First of all, two team members were stricken in Washington, within a short time of each other. They were examined by competent specialists who arrived at no conclusion. They admitted they were unable to diagnose the ailment. The possibility of an unknown disease was considered briefly, but not seriously. The possibility of a chemical agent--a drug, if you like--also was considered. This possibility has not been entirely rejected. However, a detailed laboratory investigation disclosed no trace of chemicals in the patients, apart from chemicals that were expected, of course." "Could there be chemicals that left no trace?" Scotty asked.