Flash for Freedom is, the third installment of the "Flashman Papers" supposedly discovered late in the 20th century and published by George MacDonald Fraser, detailing Flashy's fantastic career. This volume is about Flashy's involvement in the international slave trading of the late 1840s.

Fresh home from revolutionary Europe and soon to be a father for the first time, Harry Flashman believes that he has the qualities of character needed in a politician and allows his scheming father-in-law, John Morrison, to showcase him. The event goes bad when Flashy tries to seduce beautiful Fanny Locke and nearly kills an old army colleague who charges him with cheating at cards. Seeing an opportunity to get Flashy out of Elspeth's life, Morrison signs him aboard Balliol College, a slave ship.

Under the crazy and cruel, Latin epigram-quoting Capt. Spring, Flashy voyages from France to Dahomey to Roatan. As supercargo, he is responsible for housing, feeding, and exercising the slaves. Approaching Cuba with only a handful of slaves aboard, they are interdicted by the U.S. Navy and Flashy assumes the identity of an undercover British officer who had died in his arms, and convinces the Navy that he has vital information that can end the slave trade. Flashy is rushed to Washington, DC, where he insists he must divulge his information first to the Admiralty.

Returning to New Orleans, Flashy escapes the Navy's clutches to a whorehouse before being shanghaied into the Underground Railroad to escort an important runaway to Canada, gets himself condemned to slavery by seducing a plantation owner's wife, and escapes a sealed slave wagon with a wily runaway named Cassy. During this period, Flashy shows cruelty as a slave driver and learns much about the institution as Cassy lays out plans for him to pretend to sell her to get traveling money. Knowing the law is on their heels, they get as far as Portsmouth, OH, before being uncovered, and dramatically flee across the frozen river. In Portsmouth, they are taken in by abolitionists and personally defended by Abraham Lincoln, who Flashy earlier meets in Washington. Lincoln insists that it is Flashy's duty to return to New Orleans to testify. During the hearing, Flashy testifies "scrupulously" and blusters much, and the verdict, amazingly, goes in Capt. Spring's favor. Flashy blackmails Spring into conveying him home to England and is surprised to hear his real name being used again.