Harrison Chase was a wealthy aristocrat and plant collector who lived in England. He loved plants more than humans, and often wore gloves to limit his physical contact with them, preferring to only touch plants barehanded. He considered it his mission to assist the plant life of the Earth, and his personal collection of plants boasted a number of rare species.
When Richard Dunbar brought him information about a pod found int Antarctica by scientists working for the World Ecology Bureau, Chase couldn't resist adding a one-of-a-kind plant to his collection. To this end, he sent his henchman Scorby and botanist Arnold Keeler to Antarctica to acquire the pod, and paid Dunbar a large amoung of money for his information, keeping him on to be his eyes and ears inside the World Ecology Bureau.
Scorby and Keeler returned successfully with the pod, but warned Chase that there had been another, and it had infected one of the scientists, Charles Winlett, with a parasitic weed and turned him into a monster called a Krynoid. Rather than being put off, Chase became intrigued by the concept of a parasitic plant, and instructed Keeler to cultivate the pod, over the botanist's objections.
When the Doctor returned from Antarctica, having survived Scorby's efforts to kill him, Chase attempted to have him killed. He sent his limousine for him and Sarah Jane Smith, instructing the chauffeur to kill them, but he failed and the Doctor stole the limo. He and Sarah drove to Chase's mansion and the Doctor got past the gate guard by disguising himself in the chauffeur's hat and coat. However the moment he and Sarah got out, the guards realized they'd been tricked, and the two were quickly captured.
Chase decided to have Sarah be the one to get infected with the Krynoid, but thanks to the interference of the Doctor, Keeler was stung instead. Chase and his butler Hargreaves locked the mutating Keeler in an upstairs room and fed him raw meat while he changed into a Krynoid. Eventually transforming fully, the Krynoid broke free and began to rampage around the estate, killing Dunbar. Chase, for his part, went out intending to photograph the monster, and it attacked him until he stated his intention to help it.
The Krynoid spared Chase, who thereafter acted as the Krynoid's human agent inside the mansion, helping to foil the Doctor's attempts to deal with both the Krynoid and its plant minions. When UNIT arrived, using weed killer against the plants, an enraged Chase knocked out Sergeant Henderson and put him through a compost machine, killing him. He later attempted to do the same to Sarah, but she was rescued by the Doctor.
Chase fought with the Doctor and fell into the compost machine, himself. The Doctor, despite all that Chase had done, attempted to save him, but all Chase did was attempt to drag his enemy into the grinder with him. The Doctor finally abandoned his efforts to rescue his foe, and Chase was killed by his own machine.