Synopsis: The Tenth Doctor, travelling alone, lands in a practical laboratory under a biodome. There, research is being conducted on genetically altering crops so that they grow under very low-light conditions. The scientists there hope that by creating light-insensitive crops, colonists in any situation, on virtually any planet, will have the ability to be self-sufficient with relative ease.
Unfortunately, one of the scientists there is actually on the payroll of another firm, Weapontek, which wants to co-opt the research for military purposes. They intend to alter the DNA coding such that the plants can be turned into weapons. As the Doctor uncovers the plot, Brask makes his escape. To ensure a smooth departure, he powers down the biodome's sunlight shading technology. As a result, the plants receive direct sunlight, grow to enormous proportions, and instantly threaten the Doctor, Professor Flynn, and the rest of the technicians in the biodome . . .