A little late at this one but nearly there! I seem to have found several websites giving the chessboard for the theme which are all different. However, as I have the 25 squares mentioned by son1ofrover1 I shall assume that I am correct.
However, can anyone please explain 22 across? I assume that it must be EMU which works only if hysteria=fume. I cannot confirm this from Chambers. Any help please.
I thought that perhaps the answer could be EAU (= a runner/river) but I cannot parse this either!