Duel in Isengard

This was a wizard's duel that Saruman the Many Colored and Gandalf the Grey participated in. Saruman bested Gandalf (despite Gandalf having Narya) and the result was the capture of Gandalf. Gandalf was a prisoner and was to be sent to Sauron, but the timely intervention of Gwaihir (thanks to Radagast) ensured Gandalf's escape from Orthanc.