Sept. 6-15. After a series of flops, a Broadway playwright receives a script from a student that may change his fortunes. Suspense mounts steadily as the plot begins to twist and turn with devilish cleverness. Performances are Thursdays-Saturdays at 7:30 p.m.; with Sunday matinees at 2 p.m. Seniors in high school and those age 65 and older receive a special discount of $5 admission to the Sept. 15 performance.