When Induced Amnesia enters the battlefield, target player exiles all cards from his or her hand face down, then draws that many cards. When Induced Amnesia is put into a graveyard from the battlefield, return the exiled cards to their owner's hand.
If Induced Amnesia leaves the battlefield but isn't put into a graveyard, the exiled cards are lost forever. They won't be returned if another Induced Amnesia is put into a graveyard, even if that Induced Amnesia is represented by the same card.
If Induced Amnesia leaves the battlefield before its first ability resolves, its second ability will trigger (if appropriate) and do nothing. Then its first ability will resolve, and the exiled cards will be exiled indefinitely.
There are many important moments in the story, but the most crucial—called "story spotlights"—are shown on cards. These cards have the Planeswalker symbol in their text box; this symbol has no effect on gameplay. You can read more about these events in the official Magic fiction at http://www.mtgstory.com.