The entire sentence is something along the lines of "In the midst of [a period of?] chaos to which none can see an end, a single young man will embark upon a journey."
いつ and 終わる mean "when" and "to end" respectively.
*れぬ verb conjugations mean "unable to", similar to *られない, so しれぬ (知れぬ) would mean "unable to know/discern/see", and とも is used to link the two together with the impression of certainty.
Last edited by Jazzu; March 18, 2012 at 03:13 PM.