Placing his right boot squarely against a dark patch of the damaged coral, the Doctor pushed firmly. The side of the hill gave a little. Not like soft earth, but like the skin of a thick rubber dinghy. He pushed harder.
Coral crumbled away, exposing the taut oily surface of what the Doctor identified as a large, malignant cyst. Exerting more pressure with his foot, he felt the coral give way, bursting inwards as his foot disappeared inside.
"Gaah!"
A thick putrescent goo seeped from the hole as the Doctor pulled his foot clear, allowing a steady flow of vitreous pus to weep over the ground. Producing a small empty jar from his pocket, he proceeded to unscrew the lid and secure a sample of the dark, foul smelling jelly.
"I could do with the TARDIS lab, just about now," called the Doctor to no one in particular. Wherever it was, he was sure the TARDIS would hear him. Peering into the mist, he strained his ears, desperate to catch the sound of his returning ship.
Instead, he heard something else. A whisper. Unable to pinpoint the sound, the Doctor quickly realised that its rising and falling was in perfect alignment with the odd tingling sensation in one of his trouser pockets.
The sonic screwdriver.
Pulling out his trusty tool, the Doctor noticed that its ceramic grip was rotating, and that the shape was slightly different to what it had been when it took its new form. The Doctor hadn't given much thought to his last regeneration, nor to the fact that the TARDIS had completely reconfigured the screwdriver while he had other things on his mind. Examining it now, the Doctor realised that the device had something of the TARDIS about it. Between the head and the handle there now appeared to be a crystal cylinder which looked, so far as he could make out, like a miniature version of the ship's time rotor.
"Fantastic," said the Doctor, seeing the change to the screwdriver as evidence of the ship's presence nearby, "she's turned you into a psionic screwdriver. Hah!"
Holding up the jar the Doctor flipped on the screwdriver, playing its blue light across the glass. It was as he thought. The handle of the screwdriver was relaying information directly into his mind, just as if he were interfacing with his ship's telepathic circuits.
"It's a mutagen," he noted, analysing the data. "Someone's been here."
Casting his eye around the base of the hill, it took the Doctor only a few moments to spot the canister, now sinking into a pool of gunk. Reaching down, he wiped away the oily gel to read the label.
Lupus malignens delta, CX/73B/66097, New Earth"Curiouser and curiouser," he muttered, recalling a time when he'd spent four months in the TARDIS lab curing himself of a similar virus, Lupus malignens alpha. That particular strain had targeted humanoids, but this…who'd want to breed evil TARDISes, and for what purpose?"