Lord Charlie Mortdecai, portrayed by Johnny Depp, is a dubious art dealer with a penchant for swindling. His troubles escalate when he confronts a gang member named Fang in Hong Kong, only to be rescued by his loyal manservant, Jock, played by Paul Bettany. After their narrow escape, Mortdecai and his wife, Johanna, played by Gwyneth Paltrow, return to London, burdened by a staggering debt owed to the UK tax authorities.
Seeking a solution to their financial woes, they become embroiled in the illegal art scene when a valuable painting by Francisco Goya becomes the focal point of a bizarre theft that ends with the deaths of an art restorer and a thief. Enter Inspector Alistair Martland, portrayed by Ewan McGregor, who enlists Mortdecai's help due to his extensive contacts in the art world. Martland harbors feelings for Johanna dating back to their college years, adding an emotional layer to the investigation.
Martland suspects the involvement of Emil Strago, a notorious terrorist, which garners the interest of security agencies. Mortdecai agrees to assist him, hoping to claim 10% of the insurance money. He soon meets Dr. Graham, a respected art critic, who becomes intrigued by the missing Goya related to the murder. However, when Mortdecai remains tight-lipped about his client, Dr. Graham contacts Romanov, further complicating matters.
As Mortdecai conducts interviews with various art affiliates, he encounters Spinoza, an art smuggler who ends up being shot by Strago during their heated exchange. Narrowly escaping, Mortdecai analyzes crime scene photographs and deduces that the restorer must have uncovered something significant while working on the Goya—a theory linking it to a Nazi general's hidden wealth.
Complications arise when Johanna connects with The Duke, a figure who sheds light on the painting's connection to a stash of Nazi gold. Before long, Mortdecai finds himself kidnapped by Russian thugs working for Romanov, who wrongly believe he possesses the painting. Ingeniously, Mortdecai escapes, with Jock's timely help.
In a twist of fate, Mortdecai is sent to America by Martland, who desires time alone with Johanna. While trying to sell his cherished Rolls-Royce, he discovers the stolen Goya hidden within it. The plot thickens as he learns that Krampf, a potential buyer, plans to display the painting at a party. Jock suggests a heist to reclaim the painting, but chaos ensues when Krampf's daughter, Georgina, tries to seduce Mortdecai while Strago attempts to steal the artwork.
As Mortdecai and Jock race against time to recover the Goya, they face numerous challenges, including danger from both Strago and Romanov. The situation escalates as they discover that the painting previously thought to be genuine is actually a counterfeit. A scheme is hatched to disguise the authentic Goya as another piece to fund their debts in a high-stakes auction.
The auction draws attention from both Fang and Romanov, while Strago's nefarious plan to kidnap Johanna unfolds. Bidding for the Goya reaches a staggering $30 million, ultimately won by Romanov, much to Mortdecai's dismay. Although their debts are settled thanks to Martland, it turns out they've been duped again—rendering them still broke with another fake painting on their hands. As Romanov plots his revenge, the adventure takes a perilous turn, leaving our protagonists in a precarious situation.
