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

1-8
: 2s+3s Petronella turn into centre & set to partner (Men BtoB), 2s+3s 3/4
  turn partner RH & dance RH across 1/2 way to change places & end with
  other partner in prom hold (2M+3L facing Men's side & 3M+2L facing
  Ladies' side)
9-10
: 1s & 4s Petronella turn into centre **while** 2M+3L dance out & up on
  Men's side & 3M+2L dance out & down on Ladies' side
11-12
: 1s & 4s set to partner **while** 2M+3L/3M+2L cross to other side passing
  between 'gates' (1s & 4s)
13-14
: 1s & 4s 1/2 turn RH into prom hold (1s facing Ladies' side & 4s facing
  Men's side) **while** 2M+3L/3M+2L dance down/up sides
15-16
: All Promenade cl'wise 1 pl to end in square set (1s on Ladies' side
  facing 4s on Men's side, 2M+3L in 4th pl face up as 3M+2L in 1st pl
  face down)
17-24
: 1s+4s dance 1/2 Ladies' Chain (across) , 2s+3s dance 1/2 Men's Chain
  (up/down). 2s & 3s end with Lady on Man's left
25-32
: All set in square set & circle 8H round to left, dance into centre, turn
  right & spiral out to own side lines ending 2 4 (1) (3)