Serving as Head of the London Station of the American Central Intelligence Agency (CIA) is Jeff Ross. The relationship between the CIA (which has more resources) and the SIS (which has more freedom of action) is considered a special one, pivotal to multiple episodes. Ross and Burnside are friends but are forced to work against one another on occasion; for example, when Ross sends his wife, a former CIA field agent, to seduce a British official, or when Ross uses SIS to mount a dangerous rescue behind Russian lines. During the second series Ross is assisted by Karen Milner (Jana Shelden), a CIA field officer who works with SIS from time to time and is romantically interested in Burnside.