When you return to the mainland after beating the third dungeon (Moonlit Grotto), Impa will be in front of the Black Tower with a bird. Apparently, Zelda to Labrynna too soon and was kidnapped by Vires (Oh no). In a true testament to Nintendo nostalgia, go inside the tower to find ou are participating in a Donkey Kong-esque sequence.

What happens is you need to reach Zelda at the top while dodging the fireballs that roll down from Vires. Equip the Roc's Feather and jump over the fireballs. If you're at a ladder, the fireball will go down the ladder. So, stand at the edge so they go over the eldge and you can climb up the ladder without harm- the classic fake out.

When you reach Zelda's "cage" Vires will curse at you in that dramatic super villain fashion and fly away. Zelda and Impa will then head to Naryu's house and you can continue in your adventure.