A/N: Post episode/serial: "Enlightenment" from season 20.
The diamond was actually the conduit to enlightenment. When Turlough slapped it away he had a second of clarity. What he saw in that moment left him questioning.
Laying in his bed in the TARDIS Turlough stares up at the ceiling, trying to sort through his thoughts.
Since he met the Doctor he's been questioning how a species so outwardly similar to his own can be so different biologically.
Before the Doctor he had never heard of a species with a full body regeneration cycle in response to physical damage. Regeneration of limbs. Yes. Or metamorphism in response to it.
The Time Lords' regeneration cycle might be comparable to a metamorphism, but if so, it is not similar to any other that Turlough have heard about.
All species that he know about that posses the capability to metamorph are far from humanoid. So that the Time Lords could have kept such a basic physical shape yet evolved to regenerate is more than improbable.
Then there is the TARDIS design. The control station seems to be made for several people to operate, yet there are no clear partitions between stations or sections. From trying to fly the TARDIS on his own Turlough learned that this makes it verging on impossible to steer by oneself.
While watching the Doctor manipulate the controls he can see him struggle, but sometimes when he pays particular attention, it almost seems as if switches and gears, move and turn on their own. As if someone is helping. Or something...
Suddenly he was surrounded by looming white tendril. Reaching out for him from the Doctor. But when he looked at the Time Lord his shape was blurry, non distinct. Seemingly shifting in and out with someone, something else, taller and paler.
Sitting up Turlough stares down at his hand as he recalls what he saw a split second after touching the diamond holding enlightenment.
Standing Turlough flexes his hand open and closed a couple of times, before looking back up and determinedly heads for the control room to talk with the Doctor.