The Breaking of the Fellowship (Part 6) campaign card, under Resolution, says: If Fallen into Evil is attached to a hero, add that hero to the list of Fallen Heroes in the Campaign Log.

But I can't find that card, or any reference of it on other cards, or databases. Can someone explain this?

It is a Treachery from the Breaking of the Fellowship encounter set.

http://hallofbeorn.com/LotR/Details/Fallen-Into-Evil-RD

Ah, I assumed it was a burden card. And was playing on easy so it wasn't in the deck I played with. Thanks.

That is one nasty Treachery.