A Tale of Two Cities, by Charles Dickens.

British barrister Sydney Carton lives an insubstantial and unhappy life. He falls under the spell of Lucie Manette, but Lucie marries Charles Darnay. When Darnay goes to Paris to rescue an imprisoned family retainer, he becomes entangled in the snares of the brutal French Revolution and is himself jailed and condemned to the guillotine. But Sydney Carton, in love with a woman he cannot have, comes up with a daring plan to save her husband.