A Third Doctor audio story featuring Caroline John as Liz Shaw, with, unusually, two guest actors (Joe Coen and Kyle Redmond-Jones) playing UNIT troops brought in to help her penetrate the mysteries of an alien computer, leading her to quite an interesting and well-played ethical dilemma at the end. A one-idea piece but the idea is a good one and Caroline John is in command of her material. Written by Eddie Robson.