The Return of the Pink Panther

The bumbling French Inspector Clouseau (Peter Sellers) has been temporarily demoted to beat cop by his boss, Chief Inspector Charles Dreyfus (Herbert Lom), who despises Clouseau to the point of obsession. However, the French government forces Dreyfus to reinstate Clouseau as the Inspector of the Sûreté (as they had been planning to anyway, much to Dreyfus' chagrin) so that he can go to the fictional Middle Eastern nation of Lugash to investigate the theft of the fabled Pink Panther diamond, which has once again been stolen.Clouseau's investigation at the Lugash National Museum, which he nearly destroys with his klutzy ways, lead him to believe that Sir Charles Litton (Christopher Plummer), the notorious Phantom, is re-creating the most infamous heist of his career. Clouseau is delighted at this, and sees this as his only chance to get his revenge on Litton for framing him and temporarily sending him to prison (in the first Pink Panther film). Although Clouseau fails to uncover any leads into the theft, his bumbling allows him to survive several attempts on his life by a mysterious assassin. After staking out, and nearly demolishing, the Litton Manor in Nice, Clouseau is tricked into leaving France. He follows Sir Charles' wife, Lady Claudine (Catherine Schell) to a resort hotel in Gstaad, Switzerland, where his attempts to investigate her repeatedly fail.Meanwhile in England, Sir Charles reads about the theft and realizes that he has been framed. He goes to Lugash to investigate, encountering various underworld figures of old acquaintance, and foils several attempts on his life. Litton eventually manages to discover that the thief of the diamond is his wife, Lady Claudine. Because they were both bored with their quiet retirement, she stole the diamond for her own excitement, then sent her husband on a wild goose chase for his. Sir Charles makes a daring escape from Lugash and goes to Gstaad to find his wife and the diamond to clear his name.Inspector Clouseau, who has unknowingly been on the trail of the real thief all along, receives a telephone call from Chief Inspector Dreyfus telling him to arrest Lady Claudine. However, when Clouseau calls Dreyfus back to ask why, he is informed that Dreyfus has been on vacation for the past week. Dreyfus, now revealed as the assassin trying to kill Clouseau, prepares to shoot him with a sniper rifle as soon as he enters Lady Claudine's room.Lady Claudine playfully confesses the theft to her husband, and hands the diamond over to him, so he can go about proving his innocence. They are cornered by Colonel Sharky (Peter Arne) of the Lugash Secret Police, who intends to kill both of them. It turns out he has been using the theft of the diamond as an excuse to purge his political opponents. Just then, Clouseau barges into the room to arrest the Littons. Sir Charles points out that Colonel Sharky is going to kill them all. Suddenly, Dreyfus opens fire on the room, and manages to accidentally kill Sharky while aiming at Clouseau, who has ducked at the last minute to check his fly. During the fray, Clouseau is forced to allow the Littons to escape.For his work in recovering the Pink Panther, Clouseau is promoted to Chief Inspector, and vows to bring Sir Charles, who has resumed his crime spree, to justice. (Note: Lady Claudine's fate is not revealed, but it is implied she was not arrested.) Dreyfus is committed to a lunatic asylum, where he is straitjacketed and placed inside a rubber room, vowing revenge on Clouseau.

Question: What is stolen by the thief?
Answer: The Pink Panther Diamond