It often happens on this project that we script two episodes back-to-back, but they end up getting separated as other episodes come in between.  A case in point was that Episode 25 was planned before the second half of Chapter II was sorted out, and at one point we thought it would be the 23rd strip - but then Tim came up with another idea, which led to the following piece of concept art:

Episodes 23 and 25 in draft, by Tim

We then agreed that Tim's introductory panels would work perfectly well as a separate strip (i.e. they became a new Episode 23), and the last panel would stay as a self-contained episode in its own right, briefly identified as 'Episode 24'.  And then, despite having begun life as a single strip, even this pair managed to get separated as Tim added what became the actual Episode 24, and decided that it should be presented in between the two window strips.

Note also the interesting interpretation of the outside of the Fort.  It's partly based off my own comments ('Blah, something half-way between a starship and a mediaeval castle, blah something'), but we've since agreed that the Fort probably doesn't look like this drawing.  Not that we've worked out what it does look like, mind you...