Inexplicable malfunctions and behaviours in the coastal control hub for a number of deep-water drilling platforms leads the Doctor (Patrick Troughton) to believe that something menacing from the abyss has been disturbed. Need-less to say, other than companions Jamie (Frazer Hines) and Victoria (Deborah Watling in her last seral), no one believes him. The story has a strong beginning (the open scene of the TARDIS' arrival is novel) and initially sets up some nice claustrophobic tension but, as the plot unfolds, it makes less and less sense, and the sudden, and extremely convenient, 'reveal' of the killer kelp's weakness makes for an abrupt and unsatisfying ending. This serial introduces the Doctors iconic 'sonic screwdriver (although at this juncture the soon-to-be hyper-versatile gadget seems to be simply what its name implies). All of the original episodes were disposed of by the BBC so this is a fully animated recreation set to original audio recordings. Like the other recreations I have seen, the animation is simplistic (especially when the character is in motion) but serves to move the story along. Although some hints can be found in surviving stills and scraps of video, imagining what the original images (especially the special effects) is difficult.