The Daisho and the Ninja is a d20 System scenario for 1st- to 3rd-level characters. Part of AEG's Adventure Keep line of short, cheap modules in half-sized format (4-1/4"x11"), it is intended to be run as a single session. From the back cover:

The ancestral swords of a powerful lord have been stolen! In the dark of night, on the eve of battle, a shadowy figure crept into Lord Kunemura's chamber and made off with the most potent symbols of his power and lineage. Worse, Lord Kunemura has declared war on his old enemy, Lord Shotokami. The imminent battle will be decisive, and the future of Lord Kunemura's lands and family hand in the balance.

The loss of the swords would be a terrible blow to morale if Lord Kunemura's troops hear of the theft. The lord's chamberlain, Tsuyokaze, begs you to recover the swords at any price. According to Tsuyokaze, the chief suspect is the Kunemura's chief historian, Hanashi, who was suspiciously absent on the morning after the theft.

Three servants were killed during the theft, and others whisper of seeing a ninja.

Find the thief and the stolen swords before it is too late!