The Dalek test subjects were created to download the collective information of the wetworks facility of the Library on Kar-Charrat into one, single Dalek who would aid his species in their plans of conquest.
When the Scientist Daleks began to download it into the first test subject, the machine malfunctioned and the test subject went out of control. With too much information, it became insane and mad with power. Hurtling off into the corridors, the Dalek screamed in agony and fired at random as its fellow Daleks pursued it.
As the Daleks brought in the Seventh Doctor, the sickened librarian Elgin had no choice but to connect the Doctor to the retrieval interface, and the Daleks prepared to download the wetworks' data into a second test subject. This time, the natural neural buffers within the Doctor's Time Lord brain were capable of handling, filtering and compressing the rapid data flow, and the Dalek test subject survived — and acquired the accumulated knowledge of the entire universe. But the agony was too much for the Doctor to bear, and the grief-stricken Elgin discovered that the process had killed him. As the Dalek test subject assimilated the knowledge it had acquired, the Dalek Supreme returned to the mothership to report the success of the operation... and to prepared to destroy the Kar-Charrat facility behind them.
The second test subject, on the run in the library of Kar-Charrat, set fire to an explosive that Ace had planted, refusing to let it harm her. As the Daleks opened fire on the rebellious test subject, the Doctor set the data retrieval unit to download at the moment the explosives blow, and retreated to the TARDIS with Ace.
The Dalek Supreme retreated to the mothership and fled, and although the second test subject was finally destroyed by a Special Weapons Dalek Scout Seven, the remaining Daleks had no time to defuse Ace's explosives. The data storage units triggered a download just as the tanks were smashed open by the explosives, and the Kar-Charratians were freed at last. The remaining Daleks were drowned within their casings by the vengeful Kar-Charratans. The Dalek Supreme was forced to retreat, and to report failure to the Emperor Dalek. The infuriated Emperor ordered it to place the Chief Scientist in command and to self-destruct; it obeyed. (AUDIO: The Genocide Machine)