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

1-8
: 1s+4s set advancing, turn partner 2H; dance out of ends & cast into
  centre (2s/3s step up/down), 1s+4s turn partner 2H to face up/down in
  prom hold
9-16
: 1/2 reels of 3 across, 1s pass 2L RSh, 4s pass 3L RSh; 1s+4s pass RSh to
  dance 1/2 reel of 3 across with other couple. At end 1s & 4s turn
  inwards to form lines across 4s between 2s (at top) facing down, 1s
  between 3s facing up (Men on right)
17-24
: 4s+1s dance RH across & LH across back [Optional: 2s+3s dance R&L round
  4s+1s starting crossing RH on sides]
25-32
: 2L+4L+1M (top 3 Ladies' side) also 4M+1L+3L (bottom 3 Men's side) dance
  reels of 3 on sides (2L+4L also 1L+3L pass RSh to start). 2 4 (1) (3)