Segue looked like a a bolt of lightning that had been frozen in time. It could be calibrated to reach a certain destination, but the Drast were unable to choose where. When opened fully, it could destroy a planet from the quantum collapse. It was contained within a framework of chrome obelisks, shaped in an alien structures. The Drast created it using a black hole converter they stole from the Master.
The Drast planned to use the Segue to escape Earth without the Master noticing, but they were unable to aim it properly. They were forced to send humans through to see where they would end up. In the 99 tests, no survivors were brought back and no suitable locations were found. When they tried to send Griffin through, he was able to fight back and steal a gun. He threatened to break the Segue unless it was turned off. Since the Drast had no choice, they were forced to shut it down, bringing the power grid with it. (PROSE: The Story of Martha)