Superversive SF and Castalia House are probably tired of me blathering on about Death Note, so I’ll throw out my theory here. This will make sense only to people who know the story, but whatever.
I know how L could have won. Even with Light’s plan to use Rem, I know how L still could have won the game.
It goes like this:
L suspects the 13 day rule is fake, right?
Instead of testing it in front of Light and the task force, L should come in and tell everyone – Light included – that he has picked out two death row inmates to test the 13 day rule on the Death Note using a torn out page. The first prisoner will kill the second prisoner, and when he dies they will know in 13 days whether the rule is fake or not.
Now Light’s plan is forcibly delayed 13 days. Killing L will no longer accomplish anything for Misa, so naturally Rem won’t do it, since it will result in her own death.
L shows the whole thing on a live feed. The first inmate kills the second inmate, who dies on the feed within forty seconds. Now the game has started.
Imagine you are Light. There are two possibilities here. First, the first inmate was using a real piece of the Death Note and the second inmate really dies. This means that if the first inmate survives longer than 13 days Misa is put under direct suspicion again and Light himself is almost certainly screwed eventually. So the obvious answer here is to kill the inmate on day 13, solving the problem.
…Except that’s not the only problem. Remember, Light is watching this through a video feed. That first Death Note page can easily be a fake, and the second inmate could easily have faked his death. It is a heart attack after all. How would you know?
If this is the case, if the first inmate dies after 13 days this basically conclusively proves Light is Kira, because no other suspect could possibly even know who the first inmate was. If the first inmate dies, Light convicts himself. He’s in trouble. Thus the brilliance of the plan: If Light does nothing, but he’s wrong, he’s screwed. If Light kills him, but he’s wrong, he’s screwed. This all essentially relies on Light guessing directly.
What do you do if you’re Light? The answer here is that you of course need to figure out if the second Death Note inmate is actually dead. The only way to prove that is to find the original ripped out fragment of the Death Note and confirm inmate 2’s name is on it. Let’s say L hid it, but you find it, and see the inmate’s name, and independently confirm that’s his real name. Thus you’re saved – inmate 2 is dead. How do you find it?
No clue. Light has 13 days, there’s room to work. And before you say “But that’s just stupid, why would L let it be found?” just wait…
Okay. It’s the 13th day. Light knows inmate 2 is actually dead, and thus the correct answer is to kill inmate 1. He does this. So that’s that, right? Rule proven true, now Light can go ahead with his plan to use Rem to kill L. All he has to do is frame L as Misa’s greatest threat. Simple enough.
…Except L reveals a surprise: Light is wrong. Inmate 1 DID have a fake Death Note…and thus his death reveals Light as Kira. L wins!
The answer is simple: There is a third inmate.
Let’s use three terms here: The Bait, The Dummy, and Kira. The Bait is used to force Light to make a decision; he uses a fake Death Note, and on a live feed. The Dummy is misdirection. He is dead whatever happens; the important point here is that Light believes the dummy is the key to the whole thing, when in fact his death is irrelevant to Light’s response either way.
Kira is inmate number 3. At the same time as The Bait uses his fake piece of the Death Note Kira uses a real piece of the Death Note to kill the dummy, and the poor Dummy is dead either way.
Since Kira is a complete secret, there is no way for Light to stop the 13 day rule from being tested regardless. L is at worst going to put Misa and indirectly Light back under serious suspicion, and he may well have enough to arrest Misa again. But that’s not why the plan is brilliant.
What if L lets Light figure out that The Dummy really was killed? How? I dunno exactly. I mean it’s 13 days of time, give me a chance to work out a plan. But it sounds plausible.
This is why The Bait works – learning that the death of The Dummy is for real convinces Light that his only play is to kill The Bait.
And that signs his death warrant, because that means that the only person who can possibly be Kira is Light. And now L has proof. Light is toast…and incidentally L survives.