Who Magazine series overview, in issue 407 (pp26-29). The Discontinuity Guide , which counts the unbroadcast serial Shada , lists this as story number 133. Region 1 DVD releases follow The Discontinuity Guide numbering system. ^ Shaun Lyon et al. (2007-03-31). "Frontios" . Outpost Gallifrey. Archived from the original on 2008-07-31 .