Tintin in India: The Mystery of the Blue Diamond, is a 1941 Belgian theatre piece in three acts cowritten by Hergé and Jacques Van Melkebeke and directed by Paul Riga. It covers much of the second half of Cigars of the Pharaoh, as Tintin attempts to rescue a stolen blue diamond, and occurs between The Crab with the Golden Claws and The Shooting Star.
The story begins when The Maharaja and the guests enter. These include the Ambassador to Syldavie Count Koulansky, Doctor Nicholson, the nearly deaf archaeologist Chippendale, along with the latter two's wives. A telegram announces the arrival of Tintin . Count Koulansky is delighted. Since the affairs surrounding King Ottokar's Sceptre , Tintin is popularly considered a hero in Syldavia. The young reporter arrives and the soirée commences. Caudebathimouva Thoubva demonstrates hypnotism, followed by a large Indian ballet. At the end of the soirée, the Maharaja has prepared a presentation for those invited on the celebrated blue diamond. However, it is revealed that the diamond has disappeared. Tintin concludes that the thief is among the invited. Thomson and Thompson investigate, but without success. Tintin suggests that those to be questioned continue with him on the voyage to Syldavia aboard the Rampura.
Aboard the ship, Tintin questions those present during the events of the night before, but finds that one of the servants of the Maharaja has departed. Tintin decides to send a telegram before the boat arrives in Syldavia. Using the telegram, he eventually catches the thief in Chateau of Syldavia.
The second act of the piece was written by Hergé, while the other two were by Jacques Van Melkebeke. This was the first piece that Hergé had collaborated closely with another author. However, the script of the play was eventually lost and has not been rediscovered.
The play was performed at the Théâtre Royal des Galeries in Brussels, and received a positive reception from the public.