Nona has requested that you stop by the Rohirrim outpost of Stangard so she can thank Horn for speaking on her behalf.
'When we were last in this region, I was wounded in the swamp, and you brought me to the nearby outpost of the horse-lords. I was a wounded enemy to everyone there save one: the Rohirrim man called Horn. He spoke on my behalf, and when you suggested that I be taken to the Elf-woods for healing...'
You interrupt Nona at this point and tell her that it was actually Horn's idea. A confused look crosses her face.
'Really? Well, that is one more thing for which I should thank him. And that is what I want, ${PLAYER}: a brief detour to the outpost of Stangard so I can give him my thanks. Perhaps you can have him meet me here. I do not think I would be welcome once again within their walls.'
You should speak with Afic, the guard at the gate of Stangard, about meeting with Horn.
Horn is atop the hill of Stangard.
You have spoken with Afic, the guard at the gate of Stangard, and he had some inexplicably harsh words concerning Horn.
Horn is no longer welcome in Stangard, and has asked you to collect his harp from the Stangard Tavern, and his writing supplies from Wada's house.
Horn is in Stangard, waiting for you to bring him the items for which he asked.
Nona is in Haldirith, in Thinglad.
Horn has decided to travel with you, and now you should go back to Nona so she can be told.