
On the episode's website, John Romero provides exposition for Sigil: "After killing the Spider mastermind at the end of E4M8 (Unto the Cruel), your next tour of duty is eliminating the hellspawn that is causing unimaginable carnage in Earth’s cities.

Like the rest of the Doom episodes, it contains no story or cutscenes, and the only in-game story comes at the end. It takes place in Hell, and, after the final mission, Doomguy goes to Earth, to fight the demons there, in Doom 2: Hell on Earth.

The events of Sigil take place directly after Thy Flesh Consumed, the fourth episode of Doom.
