Unlike the previous two stories, this story's Unbound scenario is not immediately apparent, but as the story unfolds it is revealed to be a scenario of "What if the Doctor believed the ends justified the means?", taking the story and the character of the Doctor into darker and harsher territory than has previously been explored.
"If I told you the truth, I'd have to kill you..."
The Deep-sea Energy Exploration Project was apparently destroyed by dirty bombs in 2039 AD, turning the surrounding sea bed into a radioactive tomb. Rumours suggest the DEEP was conducting illegal, unethical experiments...
In 2066, the Doctor discovers the research centre remains intact. The terrible truth about what happened twenty-seven years ago will soon be revealed. The Doctor is determined to be the first to uncover and confront the secrets of the DEEP.
But unearthing the past can have terrible consequences for your future...
In 2039, scientist Eric Vollmer was conducting research into supplying mankind with new energy resources, but the military led by General Flint deceived him by supplying him with a research base known as the Deep-sea Energy Exploration Project so he could have access to "the black smokers," chimney-like structures on the seabed where the superheated water could provide electricity.
In truth, Flint and the military used the DEEP to hide Lee, a discredited geneticist who was conducting illegal and unethical experiments using human clones to create new supersoldiers with the unique marine life nearby.
The Doctor somehow learnt of the project conducted by Lee and Flint and sought to stop it. He reached out and contacted Vollmer, deceiving him into giving him information before Flint arrived at the DEEP to inspect the results of Lee's experiments. Vollmer discovered what Lee was doing, and when the Doctor arrived at the base Flint became suspicious. He already had his superiors guessing what was really going on and he needed to destroy the base to cover his tracks while taking the results with him.
When the base was set to self-destruct, Lee had already injected Vollmer, an unwilling test-subject, with his DNA mutagen and he transformed painfully into a mutant. The Doctor killed Lee after the scientist tried to justify his work, even comparing it to the Nazis and their atrocities since the medical data gathered later went on to save lives.
Flint was also infected by the mutagen when Vollmer attacked him and tore off his arm, and he began to transform. Flint had taken the key to the Doctor's TARDIS, and refused to give it back. With the self-destruct armed and with no time to really search for it, the Doctor had to escape in a submersible. Along the way he encountered the mutilated Vollmer, who pleaded with him to help cure his condition. The Doctor pretended to accept, but shot Vollmer and escaped.
27 years after the DEEP was supposed to be destroyed, the Doctor learnt through covert means the base was actually intact and the military were going to go to recover all research data relating to Lee's work and then destroy it.
During the time gap, Vollmer had been vilified and was used as a scapegoat for the radioactive contamination which resulted in the loss of many businesses, including Hoskins's father. Ruth, Vollmer's daughter, and her mother paid for this blame, and they had to change the family name to escape the grief.
The Doctor had been taking care of Ruth for 27 years, helping her, but when the opportunity came for her to learn more about what had happened to her father the Doctor refused to let her come down. He cited it was because of the danger, but in truth he didn't want her to come down because he would have to kill her to prevent knowledge of Lee's work spreading. But Ruth stowed away onboard the Neptune, Hoskins' submersible to venture down into the DEEP. When they were down there, Ruth learnt the truth of what had happened and that the Doctor had always known the truth of what had happened. Hoskins was killed by Flint, who had also survived the radioactive contamination. The Doctor destroyed Lee's remaining notes so no-one could find them.
Flint, terribly mutated, confronted the Doctor and Ruth, and Ruth learnt the Doctor had shot her father and learnt the Doctor's real motives for going to the DEEP were not for her, but to destroy Lee's work and to destroy the DEEP once and for all while recovering his TARDIS key. Flint showed the key and shoved it down the Doctor's throat, snapping it. Ruth watched on angrily but she held onto Hoskin's gun ready to kill the Doctor after he'd told her about his power to regenerate. When the regeneration occurred, the new Doctor barely had time to say "Hello, I'm the Doctor. Who are you?"
Coldly, Ruth shot the new Doctor, ready to kill all of the remaining lives the Doctor had to see him dead once and for all.
- The Doctor - David Collings
- General Flint - Ed Bishop
- Ruth - Siri O'Neal
- Hoskins - Jeremy James
- Professor Vollmer - Matthew Benson
- Lee - Jack Galagher
- The New Doctor - Ian Brooker
- The Doctor uses the alias "Dr. John Smith."
- The Doctor has told Ruth about regeneration.
- When the Doctor fled the DEEP in 2039, he was forced to leave his TARDIS behind. Consequently, he has been trapped on Earth for the previous 27 years.
- The Doctor manages to gain access to the DEEP using his UNIT credentials.
- Over the course of the story, the "What If" scenario is revealed to be "What if the Doctor believed the ends justified the means?", with Collings's Doctor being portrayed as a Doctor who kills as the first option for the "greater good" where the Doctor in the "prime" universe would be more willing to rely on peoples' better natures and allow them to live after making dangerous mistakes rather than killing them in case they repeated their errors.
- After Sympathy for the Devil, this is the second Big Finish audio drama to feature a Time Lord regenerating. It was the only one in which the Doctor does so until the release of Seven Keys to Doomsday in 2008. Furthermore, the Sixth Doctor regenerated into the Seventh Doctor in AUDIO: The Brink of Death in 2015.
- The regenerated Doctor at the end of the story was credited to Ian Brooker on the Big Finish website (as well as on Ian Brooker’s offical website, on which he proudly declares himself the shortest-lived incarnation of the Doctor), but was not listed in the story's printed liner notes.
- This audio drama was recorded on 19 May 2003 at the Moat Studios.
- The titles of this story and the next Unbound story He Jests at Scars... are Shakespearean references. "Full fathom five thy father lies" is a line from The Tempest Act 1, Scene 2, and is quoted directly in and is thematically relevant to the story. Both stories are also about dark and tragic Doctors.
- This story was originally released on CD. It is now available as a download only.
- In 2007, Full Fathom Five had sold enough copies for Bishop to receive royalties. To his amusement, the first cheque he received was for £4.42.
- The Doctor observes that military intelligence is an oxymoron, and gains Vollmer's confidence with the aid of his UNIT credentials. (TV: Terror of the Autons)
- Official Full Fathom Five page at bigfinish.com
- DisContinuity for Full Fathom Five at Tetrapyriarbus - The DisContinuity Guide