Sharpe's Devil is the twelfth historical novel in the Richard Sharpe series written by Bernard Cornwell and published in 1992. The story is set in 1820, with Sharpe and Harper en route to Chile to find their old friend Blas Vivar. Along the way they encounter the exiled Napoleon Bonaparte and the Scottish former Royal Navy officer Lord Cochrane. Chronologically, this is the most recent book in the series, with all subsequent novels (as of 2025) depicting earlier events in Sharpe's career.

Doña Louisa Vivar, whom Sharpe befriended in Sharpe's Rifles, visits Sharpe and asks him to search for her husband, Don Blas Vivar, who disappeared while serving as Captain-General of Chile, a Spanish possession threatened by rebels. Sharpe and Harper sail to Chile with Spanish Colonel Ruiz and his regimental officers aboard the frigate Espiritu Santo, commanded by Captain Ardiles. The group decide to stop off at Saint Helena to pay a visit to exiled French emperor Napoleon Bonaparte. Napoleon grants an audience and asks Sharpe and Harper to remain for a private conversation. Napoleon persuades Sharpe to take a gift, a portrait of the emperor, to an admirer in Chile for him.

British Consul George Blair welcomes Sharpe and Harper to the Chilean port of Valdivia and informs them that Blas Vivar's body was found and buried three months previously. Sharpe and Harper visit Captain Marquinez to arrange permission to travel to Puerto Crucero, exhume the body and return it to Spain. Back at their lodgings, they interrupt burglars who wound Harper and escape with their possessions, including Napoleon's portrait.

Sharpe and Harper meet with Bautista, who announces that he has caught the thieves, whom he has branded on the spot, and returns all the stolen goods except for the portrait. When Bautista asks if everything is there, Sharpe says nothing is missing. Marquinez provides the required passes and permits and rides out with Sharpe and Harper on the first stage of their journey. Overnighting at the "Celestial Fort", Sharpe suspects that their escort, commanded by Sergeant Dregara, has orders to kill them. He persuades the garrison commander, Captain Morillo, to let them leave very early the next morning; he provides a native guide called Ferdinand to take them safely across the hills.

Sharpe and Harper arrive in Puerto Crucero and are welcomed by Major Suarez, but before they can exhume the body, Sergeant Dregara catches up and arrests them. After five days in prison, they are accused by Bautista of espionage. He reveals that a coded message was found hidden in the back of the portrait. As punishment, the Captain-General has Ferdinand executed, confiscates the riflemen's money and weapons and has them put aboard the Espiritu Santo for its return trip to Europe.

Lord Cochrane, a highly successful former Royal Navy admiral now in service to the Chilean rebels under Bernardo O'Higgins, uses a ruse, a seemingly disabled American whaler, to get his men aboard the Espiritu Santo and, with the assistance of Sharpe and Harper, capture it, taking Captain Ardiles prisoner. The Espiritu Santo is in great danger of sinking, but Cochrane insists on sailing to the Spanish-held port of Valdivia. Fortunately, his flagship, the O'Higgins, finds them. Cochrane loads Major Miller and his marines aboard the crippled ship, and sets sail for a seemingly suicidal attack upon the port of Puerto Crucero (not Valdivia, as the Espiritu Santo would never make it there).

Cochrane and Miller lead the marines ashore, with Sharpe and Harper in tow, and with supporting fire from the O'Higgins capture the citadel. Blas Vivar's grave is opened to reveal nothing but a dead dog inside. A captured Spanish soldier informs them that Blas Vivar is being held prisoner in Valdivia, so Sharpe reluctantly agrees to join Cochrane's assault on the city.

Despite being massively outnumbered and outgunned, Cochrane sails to Valdivia, hoping his two disguised ships will be mistaken for transports bringing much-needed artillery and reinforcements from Spain. However, his ruse fails. Sharpe recommends landing on a nearby beach and leads an assault on the outlying forts. To Sharpe's amazement, the demoralized Spanish put up token resistance before either fleeing or surrendering, resulting in little loss of life on the rebel side. Without waiting for reinforcements, Cochrane marches his small forces into the city itself, where Sharpe and Harper kill Dregara. Trapped, Bautista commits suicide.