Elladan explained that the horse had been the best means to track his rider, as the Nazgûl can remain virtually unseen once they remove their cloaks. He suggested that we talk to Glorfindel in Rivendell who may be able to help us.
We travelled back to Rivendell and discussed the situation with Glorfindel. He had suspected that not all the Nazgûl were claimed by The Bruinen and asked us to take an elf-stone to the Ford and hold it aloft. It seemed like a strange request, but he is clearly wise and knowledgeable so we travelled across the Trollshaws and did as he requested. We were most surprised when the elf-stone began to glow! When we returned, we found out that Glorfindel had expected that the elf-stone would glow in places that the rider has been. We shall use this stone to try and track the rider.