The Fall Edit
Boris and Isla Kotenkov were to MI5 agents sent to Aero City, Russia in The Fall. James was later sent to them in Russia. After the two are sent for a "weapons negotiation" (in which they were supposed to gather enough evidence to arrest Obidin), they kill Dennis Obidin, but are in turn killed by his brother Vladmir Obidin, who, unbeknownst to anyone, had been paid to do so. Their deaths later cause controversy, as the MI5 blame CHERUB for their deaths, risking James' CHERUB career in the process. Eventually, James' innocence is proved, and it is revealed that Boris and Isla were bribed.
Though not much is revealed about Boris and Isla, we can assume that they are poor, as they were easily bribed into assassinated Dennis Obidin, and that they can be deceptive, as they tricked James and even alerted Vladimir about his presence.