Harris believes Robson's pride is making him refuse to shut off the gas flow in order to properly investigate the feed lines, but his calculations are mysteriously gone from his briefcase. Thinking he has left the file in his desk at home, he asks his wife to look for it and bring it to him. The file is on the desk, but when she opens it, Mrs. Harris is pricked by a sharp piece of seaweed. She falls ill, and Harris ends up asking the Doctor for assistance after Victoria has helped the travellers escape from their cell by picking the lock with her hairpin. Meanwhile, Mrs. Harris is visited by Mr. Oak and Mr. Quill, technicians from the command centre who have already been infected by the seaweed, and have long green tendrils growing along their arms and backs of their hands. The men render Mrs. Harris unconscious by attacking her with noxious gas from their mouths, then leave. Arriving after, the Doctor can't determine what's wrong with Mrs. Harris, but his suspicions are aroused by the seaweed, and he, Jamie and Victoria return to the TARDIS to study it.