It’s genuinely handy having those space-time telegraph messages! It allows the bewildered "Brigadier" (Nicholas Courtney) to call upon the "Doctor" (Tom Baker), "Sarah Jane" (Elisabeth Sladen), and "Harry" (Ian Marter) so they can return to Earth and look into the complete demolition of some oil platforms near Scotland that were thought to be unbreakable. This gives them a reason to wear their best Scottish clothes and travel north, where they encounter the "Duke of Forgill" (John Woodnutt), who owns a castle by the sea that becomes involved in this rather good mystery, which provides an unusual explanation for how "Nessie" came about. They also find out there’s been considerable cloning happening and that these creatures are naturally trying to take over the world. Will the team be able to stop this evil scheme? This story told across four episodes is one of the more enjoyable ones, with a strong script supporting a good adventure; it might lean a little too much into stereotypes about Scottish people and weather, but Baker is at his most charmingly playful, Sladen and Courtney once again show their value in supporting roles, and Lillias Walker also makes an impression (especially for a 5pm broadcast) as a nurse I wouldn’t want to meet – no matter how unwell I felt. The special effects are pretty good too, with lots of imagination put into the latex and rubber costumes, creating a unique and quite frightening villain, and it's generally an enjoyable experience.

Source on TMDB