For 35 years, one of the world's most maddening unsolved codes sat in plain sight in the courtyard of CIA headquarters, daring the entire intelligence community to crack it. Then two journalists found the answer in a cardboard box at a public museum archive.

This episode traces the strange life of Kryptos, the encrypted copper sculpture artist Jim Sanborn installed at Langley in 1990. It's a story of interagency rivalry, typos that drove solvers to the brink, a near-million-dollar auction, and the ultimate irony: a monument to intelligence gathering defeated not by brilliant cryptanalysis but by human fallibility.

• How the NSA quietly cracked the first three passages in 1992, beating the CIA's own analysts by six years
• The decrypted messages, from poetic lines about occlusion to coordinates pointing 174 feet into the CIA c ...