The Anning Tower Guard Manual

A 25-year-old graduate fills in for a month-long night shift at Anning Tower. HR's manual has a dark stain left by the predecessor. After 23:00 only one elevator runs. Don't step out on the thirteenth floor. Every shift the manual gains a rule, though no one is seen writing. Old Mr. Chen is 80 in the records, identical to a photo from sixty years ago.