Kumar, a thief by profession poses as the son of Raja Bahadur Singh to accept an invitation to the island of Sir John Locksley. The guests include K.P.W. Iyengar aka Romeo, Dr. Dubari, Colonel Columbus, and Countess Sylvia Rasmussen. A stunned Kumar finds out that all of these invitees are master criminals. Kumar's guise does not fool anyone, nevertheless Sir John permits him to stay on. The reason why John has invited them is to find a successor to take his place as he is dying of cancer. He feels that one of his invitees can be trusted to take his place and for this he has arranged for them to steal a ruby (Shalimar) worth 135 crores of rupees. This gem is placed in a secure room within his palace, which is alarmed, and guarded. He challenges one of them to steal the Shalimar - but if anyone fails then they are killed by the security system. Pitted against such veterans, it looks like Kumar has got himself into a bind that he may not come out of alive.
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