A Lay of Luthien by Himring

Chapter 4: Luthien at High Speed

There is no fastness that can keep Luthien in. There is no fastness that can keep Luthien out.

Housebreaker Luthien! Thief Luthien! Luthien, bat burglar!

Huan may be faster than Luthien and captures her, but just as quickly she captures his heart right back: fast friends.

And Morgoth? Far too slow. Those who want to catch Luthien need to get up earlier than that!

Mostly, it is herself Luthien steals away from those who would hold her fast, laying claim to her against her will.

The Silmaril is incidental. That it lays Doriath open to invasion and slaughter, thrice—unfortunate.