To celebrate King Baltras' birthday, the Seven Deadly Sins arrive at a border territory looking for an elusive ingredient, the sky fish. In the middle of searching for it, their captain Meliodas and the pig Hawk get sent up to the Sky Temple, home to the Celestials.
The Celestials hold watch over an Indura-type demon sealed in their land since the Holy War's end 3,000 years ago. But when a group of demons calling themselves The Six Knights of Black attack the Celestials and release the Indura, a Celestial youth named Solaad brings Meliodas and Hawk to his people's land while he leaves to find the legendary white pig whose power was used to seal the evil. To protect everyone, Meliodas and the others clash against The Six Knights of Black.
A novelization by Shuka Matsuda was published on August 29, 2018.
The Seven Deadly Sins the Movie: Prisoners of the Sky provides examples of:
- Floating Continent: The Sky Temple is a floating mass of land located above the clouds somewhere in Britannia. It is home to the Celestial Clan.
- Non-Serial Movie: The movie is based on a story written by Nakaba Suzuki, the author of the original manga, but it isn't part of the manga or anime canon continuity.
- "Shaggy Dog" Story: The movie has the Sins, for their original quest, hunting a variety of exotic beasts in order to prepare a special feast for King Baltras' birthday. Their adventure in the sky incidentally gets them the last ingredient for their feast. And then their quest ends in failure because they made the mistake of allowing Meliodas to cook it, causing the meal to be inedible.
- Twin Switch: A large part of the movie is about Meliodas accidentally trading places with a complete stranger who happens to resemble him. It goes on far longer than is plausible, given that the resemblance isn't all that great once you see them standing still in good light (The two may have the same height and build, and similar facial structures, but they have different hairstyles, slightly different hair colors, totally different eye colors, and Salaab has wings), plus the fact that Meliodas never even attempted to pass himself as Salaab in front of his associates, and in fact is continuously trying to ask who they're talking about as they chew him out for Salaab's actions, but keeps getting ignored.
- Winged Humanoid: Living in the Sky Temple are a race of winged people known as the Celestials, descendants of the Goddess Race who hold watch over an Indura-type demon sealed in their land since the Ancient War's end 3,000 years ago.
- The X of Y: The title is "Prisoners of the Sky".
