From light can come darkness. That's the lesson on 'Lost' (Tue., 9PM ET on ABC).

[Spoiler alert.]

Unexpectedly, the story features no time-skips (well, except for one). This episode of 'Lost' is set almost exclusively in the past, and explores the history of the island -- and the mysterious Smoke Monster.

In the distant past, a woman (Allison Janney) adopts a pair of fraternal twins -- one child is named Jacob (Mark Pellegrino), and the other child remains ominously nameless (the character is played by Titus Welliver). The woman tells her adopted sons that other humans are evil. She also shows them a stream leading to a mystical cave of light, and tells them that they will one day be the guardians of the cave.

Eventually, conflict results between the brothers, and Jacob throws his brother downstream, where he floats into the cave. In the instant after the nameless one disappears, the Smoke Monster suddenly streams out of the tunnel of light.

There's much more to it than that, and though the episode doesn't resolve many questions, it does provide another piece of the puzzle that is 'Lost.' And as the woman says, "Every question I answer will simply lead to another question." Is this a message for her adopted sons, or a message for the viewers of the show?