Claus is a famous teacher of magic residing in Euclid a hundred years before Cress Albane, Chester Burklight, and Mint Adenade are born. While researching summoning, Cress Albane and Mint Adenade come searching for his aid to defeat Dhaos. Initially dismissing their claims as a plot to obtain free lessons in magic, his assistant Milard Rune manages to convince him otherwise after a small argument. Claus decides to take them with him to Lone Valley, where the Wind Spirit Sylph resides. He explains to Cress and Mint that the art of summoning, a particular kind of magic which even humans can use, is focused around forming pacts with Spirits using jeweled rings. They find that Lone Valley's Spirits are rampaging, and Claus discovers that Miasma, demonic wind from Daemonium, is causing the Sylph to run wild. Using that knowledge, he comes up with a plan to stop the Miasma by covering the holes from which it comes with rocks, preventing them from entering. With the Sylph calmed, Claus manages to form a pact with the spirit.