Derek Cranston served in Earth Special Intelligence Division, a civilian agency directly controlled by the Office of the President of the Earth Alliance.
In 2259, Cranston was sent to Babylon 5 to track down President Morgan Clark's former physician, Dr. Everett Jacobs. President Clark had authorized both him and the station crew to use deadly force if they needed to in apprehending Jacobs. When Cranston arrived, he told Captain John Sheridan and his senior staff Jacobs was attempting to defect after having stolen highly classified information. It is unclear if Cranston knew the real reason President Morgan was wanting Jacobs found: he had some evidence implicating Clark in the death of his predecessor, President Luis Santiago.
Captain Sheridan seemingly cooperated with Cranston to try and find Jacobs, allowing him the full use of his security teams. Cranston was irritated when he found out he could integrate his scanners (programed to track a chip implanted in Dr. Jacobs) into the station hardware. Once he discovered this, he insisted it be done. Cmdr. Ivanova complied, noting it would take several hours to complete.
In the meantime, Cranston was contacted by a man in Downbelow named Max who hinted that he had Jacobs captured. Cranston agreed to a ransom demand Max asked for, but Max never turned up at the appointed place. Heading to C'n'C, Cranston's team personally begins the scanning procedures--but the scans do not find Jacobs aboard. At the same time, Ambassador Kosh's Vorlon transport leaves the station. Cranson orders C'n'C to scan the ship in case Jacobs is aboard, but no humans are detected. His search a failure, Cranston returns to Earth.