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

1-6
: 1s and 4s Petronella turn & set, Petronella turn to opp sides (no polite
  turn)
7-8
: 1s+2s & 3s+4s circle 4H 1/2 round to left & join NH with partner facing
  up and down. (2) 1 (4) 3
9-16
: 9-10 All couples set advancing to pass next couple LSh.  1 (2) 3 (4)
11-12
: End couples 1/2 turn 2H to face down/up **while** middle couples set
  advancing to pass LSh. (1) 3 (2) 4
13-16
: Repeat 9-12 to end on sides. (3) 4 (1) 2
17-20
: 4s dance 1/2 Fig 8 up round 3s **while** 1s dance 1/2 Fig 8 down
  round 2s.  3 4 (1) (2)
21-24
: 4L+1L change places RH & set **while** 4M+1M set & change places RH.
   3 1 (4) (2)
25-32
: All Adv+Ret (1 step each), cross RH with partner; 3s+1s & 4s+2s
  circle 4H round to left. End 3 1 (4) (2)