The Five Knots by Fred M. White

Russell sat unmoved; he was not acting without due deliberation, though he realised that he had a dangerous foe to deal with. For some time Uzali played with the string, tying and untying the knots as if he were making up his mind what to do next. To Wilfrid Mercer, looking on, the incident reminded him of two chess masters bent over a table.

"You are a stranger to me," Uzali said.