The overmind gained awareness. In the "alien room" of the Advanced Tactical Combat Simulator. The overmind was connected to other overminds in a hive mind collective consciousness, but was also an individual only part of the whole. It knew that it was being held captive, to train humans to fight the alien races. It had known pain, and many "deaths" of it's corporeal form. It would "die" again returning to the collective, eventually and a granger would re-form a body for it when the humans decided to train new recruits. It also knew that the humans could be killed in this place, and that they would nourish the creep, and the many "children" that were to be born. The children stirred in the overmind's "brain" wishing for bodies so they might act and feed, becoming more powerful.
A dretch was born. Expelled from the egg, it quickly realized it's consciousness, and began to feel the overmind touch it's new mind. Vaguely directed to defend the overmind, and the eggs the dretch was mostly left to act for itself, and feed itself.
A granger was busy tending creep nearby, forming acid tubes but the dretch took no notice.
Hunger drove the dretch to explore, it moved quickly out of the creep, towards the open center of the simulation area. It explored the walls, the floor, and the ceilings. It already knew the layout of the environment, and quickly, carefully probed the immediate area, knowing the danger that human weapons posed.
Sound alerted the dretch, it slid out of the line of sight, letting the human pass and then dropped down from the height, chasing silently, then leaping to the back of the human's neck, it bit. It then bit the back of the human's spine, ensuring death.
A series of sharp cracks, and rifle fire destroyed the dretch's body and it was forced to take a new body from the eggs back at the creep. But it had fed, and the human blood energized it, giving the small creature vitality even in it's new body.
The dretch touched the overmind, it received evolutional information that had been stored and modified over the centuries. It quickly restrucured it's own genetic code, forming the new tissues rapidly and became a basilisk. Exuding a pheromone that could cause rapid healing of wounds, it stalked away making a slight clicking sound as it walked back towards the entrance of the alien room to wait...