Wolf in the Fold

Kirk and McCoy take Scotty to Argelius II to recover after an explosion, caused by a woman, left him injured and resentful. When a dancer, Kara, is found murdered with Scotty beside her, Administrator Hengist demands his arrest, and under Argelian law Kirk must co-operate. More women die, and Scotty is always near the body. Prefect Jaris's empathic wife Sybo senses an ancient, hungry evil and speaks names including Redjac, before she too is killed mid-ritual. Using the Enterprise computer, Spock links the name to Jack the Ripper and to a chain of unsolved killings across many worlds. The killer is a bodiless entity that feeds on fear, and it has been wearing Hengist. Driven out, it seizes the ship's computer, until Spock occupies the machine with an endless calculation of pi. The crew are sedated so their fear cannot feed it, and when it returns to Hengist's body that body is beamed into space at the widest dispersal.