An unexceptional spy drama by Andre De Toth, Man on a String is based on an autobiography by counterspy Boris Morros, here given the name of Boris Mitrov and played by Ernest Borgnine. Mitrov was born in Russia but had been a citizen of the U.S. for some time when he joins up with a Russian spy network. He is caught out by the CIA, and they offer him a deal: go to the USSR and spy for our side, or else. Boris' boss is Bob Avery (the handsome Kerwin Mathews) and Colleen Dewhurst is Helen Benson, the lone female in the story. Clichéd dialogue aside, the scenes shot in Moscow and Berlin add convincing realism to the action.
~ Eleanor Mannikka, All Movie Guide