The Bengal's Eye is a jewel.
The Bengal's Eye is a ball-shaped diamond, rather large by rodent standards, famous for its purity and fine crafting. Under natural light, it has been shown to gleam various shades of light blue. The Bengal's Eye belongs to the rodent Maharajah of Rajkut (India).Maharajah of Rajkut visited London with his harem and some servants, and also brought the Bengal's Eye with him. During the Maharajah's stay at the Gorgonzola Hotel, the diamond was stored in a special room adjacent to the Maharadjah's suite. This room had two entrances, an armoured door and a trapdoor in the ceiling that was supposed to be locked from the inside. The diamond was also guarded day and night by two of the Maharajah's most trusted guards.
Criminal mastermind Professor Padraic Ratigan, believed to be dead at the time, lured Basil of Baker Street to the room with the maharajah. He then had his minion Fidget break and enter into the flat in another room in an intentionally noisy way; Basil, the guards and the maharajah rushed to the other room while Fidget hid himself under the diamond's hollow pedestal. After the room was sealed again, Fidget left through the trapdoor with the diamond.
Basil and Dawson, the last people to have seen the diamond, were the prime suspects, which was exactly what Ratigan intended all along; his goal was not to have the Bengal's Eye but to frame Basil in revenge for foiling his plan and nearly causing his death. The Bengal's Eye was then planted into Basil's suitcase, leading to both their arrests; the diamond was returned to the Maharajah. Fortunately, Ratigan's plan was later exposed by Basil's cunning.