Act I: A Child's Secret

First things first, make sure you've met the unlock criteria: Adventure Rank 36 and a Story Key (earned from 8 Daily Commissions). Once you're good to go, travel to the Anemo Archon Statue in the plaza in front of Mondstadt Cathedral to kick off the quest.

After the initial cutscene, your next stop is Flora's flower shop, located near the entrance of Mondstadt. Chat with her to get your next objective.

Next, you'll need to find Timmie. He's usually hanging out on the Mondstadt bridge, so head over there and see what he's up to.

After checking in with Timmie, the quest directs you to spy on the adults in the tavern. Make your way to the tavern and discreetly observe the conversations happening there.

Following the tavern scene, fast travel to the Knights of Favonius headquarters. Your objective here is to speak with Ellin, who you'll find training in the back of the building.

The final step is a bit of a challenge: you need to destroy all three training dummies at the same time. The best way to do this is to weaken them all first by hitting them with attacks until they're close to breaking. Then, use an Elemental Skill that can hit all three dummies simultaneously to finish them off.