As soon as you complete the Retracing Frozen Steps questline, you are given this questline, also by Leif.
When you send Leif to the Frost Owl Spire the first time (presumably as part of Part 2 of this quest), you receive another quest, which you'll be given as soon as you complete this one. The quest is called Remedy for Remembering.
Part 1 of 2
Part 2 of 2
Forge 1 Grappling Hook
Send Leif to the Frost Owl Spire
Find 1 Star Sapphire