Adam Colby was a scientist who, along with Maximillian Stael and Thea Ransome, worked for Dr Fendelman in studying "Eustace" at Fetch Priory. The apparently human skull was found in volcanic sediment twelve million years old. Fendelman and Stael conducted experiments together which Thea and Colby were not privy to.
In July 1977, Colby was walking Leakey in the woods adjacent to the priory when he came across a dead hiker. Returning to his colleagues, he told them of what he had found. Fendelman said they must consider, and Colby queried what there was to discuss, saying "there's a body out there. We can't just leave it. Or are you breeding vultures in that secret lab of yours?" Nevertheless, he was persuaded, despite Thea's protests, by Fendelman - who suggested that Colby's acquisition of a Nobel Prize might be compromised - that it was best if the body was moved so that their work wasn't impeded by any publicity generated.
Colby and Thea were displeased when they learnt from David Mitchell that Fendelman had a security team at the priory following the hiker's death, and that nobody could come or go without permission. Mitchell advised that they have a word with Fendelman. Colby went to his lab to find him and Fendelman entered after him. The doctor asked Colby if he was impressed, to which he replied "oh, I don't know. I always say if you've seen one jukebox, you've seen them all". Fendelman explained the time scanner's function to him.
When they were alone, Colby told Thea what Fendelman had told him - that "he actually believes that he can see into the past with that electronic fruit machine he's got down there". Thea questioned Colby on what Fendelman had said and more readily believed in the experiment, telling Adam that Fendelman was "one of the authentic geniuses in the field until he developed this interest in the origins of man". Colby replied "you mean until he flipped his lid."
Sometime later, Colby found Thea in Fendelman's lab and was unable to gain her attention despite his calling to her until he had turned off the time scanner. As he did this, a scream came from the kitchen and Colby led Thea there to find the source. They found Mitchell dead and, when Thea's only response was to comment "there's a blister on the back of the neck. Could be a birth mark, I suppose", he questioned how she could be so dispassionate with a man being dead. Thea collapsed to the ground and, as he entered, the Fourth Doctor warned Colby not to touch the body. He asked Colby how many deaths there had been and Colby told him it was the second. The Doctor that the creatures that appeared above Thea as she glowed brightly looked like embryo Fendahleen. The Time Lord warned that within a year, if he was right, there would only be one person left on Earth. Colby asked the Doctor who he was - "some sort of wandering Armageddon peddler?" Fendelman and Stael entered and the former ordered that the Doctor be locked up. This time, Colby said, he would call the police. As he left, Fendelman asked him how he would explain why he had not called before.
Alone again, Thea asked Colby why he had agreed to not call the police in the first place, and he told her he had always been ambitious, which he said was a weakness in anyone. Thea agreed, adding "particularly scientists." Thea suggested he call the police now, but when he tried the phone, Colby found it had been disconnected. When Thea asked if he was serious, he replied "I am serious. The place is surrounded by guards, we're beset by a wandering lunatic and we have a pair of corpses on our hands. And on top of all that, the telephone seems to be very dead. Thea, we're trapped." Thea responded that it was planned and Colby asked if she meant by Fendelmen, but she said no - he was doing what was planned for him. Thea asked him to ask her who had planned it, but he wouldn't, so she told him she had. Adam told her she was "as sane as anyone here", somewhat doubtfully.
Going to Fendelman, Colby confronted him about disconnecting the phone and called him mad. The doctor asked him to sit and began explaining his theory that Eustace had an extra-terrestrial origin. Colby was disbelieving and realised that Fendelman thought all humans were descended from aliens. In the kitchen, Fendelman told Colby, with Thea present, that he had been working secretly with Stael. Thea left them, claiming she was tired. Fendelman showed Colby the x-ray's he had taken of the skull showing a pentagram on it and said he believed this was where the energy the skull contained was stored. The release of this energy was be a signal to the extra-terrestrial predecessors of humanity that there was intelligent life on Earth.
Fendelman used the time scanner in an attempt to convince Colby of his theory. Adam thought the doctor's comclusion was rather illogical. As they were discussing this, Stael entered and threatened them with a gun, ordering them to turn off the scanner, which Colby did. They were taken prisoner and tied to separate pillars in the cellars of the priory, with Thea unconscious on the ground nearby, lying on a pentagram.
Fendelman asked how long he had been planning this and Colby replied that it was ever since Martha Tyler's visions began. Fendelman questioned how he could believe such a thing, given his "first class brain". Colby reputed this claim, saying, "first class brain? He's an occult freak. One of those feeble inadequates who thinks he communes with the devil." Stael replied "unlike you, I am not a crude lout, Colby. The grimoires do not impress me. Mrs Tyler's paranormal gifts and the race memory she draws on, these were the signposts on the road to power". He told Colby he looked forward to his terror.
When he realised Stael's intention, to couple the time scanner with Eustace and, Max believed, gain immense power, Fendelman cried out for him to stop, despite Colby asking him not to, and Stael shot the doctor, killing him. For this, Colby branded him a "murdering lunatic". Colby watched as Thea was transformed into the Fendahl core and began killing the members of Stael's coven who had assembled.
The Doctor and Leela entered the cellars and cut Colby lose. He told them the other couldn't be left behind, but the Doctor was unable to help Stael, who couldn't move and committed suicide. In the hallway of the priory, Colby found Martha and Jack Tyler and blamed for former for what had happened and labelled the latter a "swede-bashing cretin". Leela told him to be quiet as he had almost got them killed in the cellars, a point the Doctor reiterated when he joined them.
The Doctor explained to Colby and the others that the Fendahl - the creature that had influenced Thea - was a gestalt organism, made up of twelve Fendahleen and a core, which was Thea. As one Fendahleen was dead and Stael killed himself, the creature was incomplete. Colby questioned the Doctor on the origins of the Fendahl and he explained that, on the homeworld of the Fendahl, evolution had, as Colby put it, "turned back on itself" and a creature that ate life had come into being. The Doctor said he did not think the skull created man, but that it may have had some effect on his evolution.
The Tylers returned to their cottage and the Doctor asked Colby if he would stay and, after giving Leela and him adequate time to reach the cellars, turn on the scanner beam. In the confusion, he would retrieve Eustace. He told Colby to run the beam for two minutes and then flee as, after a further three minutes, a controlled explosion he had rigged was go off, destroying the priory. Colby did this and provided the Doctor with the time to retrieve the skull from the altar in the cellar which the core was afflicted by the beam and the salt hurled at it by the Time Lord and Leela. This done, he left the priory and sheltered with the Tylers in their cottage as the priory was engulfed by the flames of the explosion. Leela asked the Doctor if it was okay to leave the others, and he told her "Yes. Probably at Mrs Tyler's now, eating plum cake off her best china." (TV: Image of the Fendahl)