Having a description of athelas's scent makes tracking it down incredibly easy. It pays to have a best friend with an excellent sense of smell.

Hiccup lets the crushed plant's leaves fall into the boiling water, and an entirely different scent from the original sweet smell hits his nose. The smell of an isolated cove on a northern island wafts over him, and it's clear that the athelas is much more than it appears.

Hiccup brings the water over to Sothe, letting the steam drift over the boy.

"Sothe? Sothe, can you hear me? You need to wake up."