{{explanation}}
3s & 4s start on opposite sides

1-4
: 1s & 4s dance 1/2 Fig of 8 round next couples
5-8
: 1L also 4L cross diag to dance out between 2s & 3s, cast to right &
  cross to other side **while** partners follow to end at other end of
  set (opposite partner)
9-16
: All dance reel of 4 on sides
17-20
: 2M & 3M dance out & cast round end dancer, dance across set & cast 1
  place on other side as ptnrs follow - crossing & casting to R - but
  dance down/up 1 pl on opp side to ptnr, when 2M & 3L also 3M & 2L
  approach each other they pass RSh & Lady turns in behind passing Man
  (not her ptnr)
21-24
: 3M & 2M (followed by 2L/3L) dance up/down between end couples, cast to
  right & dance into original places
25-32
: 4s+2s also 3s+1s dance Tourbillon :

: 4s+2s also 3s+1s 1/2 turn prtnrs 2H, 4M/2L also 3M/1L lead prtnrs 1 pl
  cl'wise to end 4s/3s on Ladies side & 2s/1s on Men's side, 4s/3s set
  to 2s/1s

: All 1/2 turn prtnrs 2H, 4L/2M also 3L/1M lead prtnrs on 1 pl to end
  2s/1s in 1st/3rd pl & 1s in 2nd/4th pl & all cross RH to own sides to
  end 2 4 (1) (3)