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

1-8
: 1s & 4s Petronella turn & set, turn partners RH into prom hold facing
  2M/3M (2s & 3s having stepped up/down)
9-16
: 1s+4s dance 1/2 RSh diagonal reel of 4 with 2M/3M & end facing other
  couple, 1s+4s set & turn other partner RH to face 2L/3L
17-24
: 1s+4s dance 1/2 RSh diagonal reel of 4 with 2L/3L & end on sides in
  order 3 4(1)(2), 1s+4s dance 1/2 R&L to end 3 1(4)(2)
25-32
: All set forming a circle, cast (2 PdB) & chase clockwise 1/2 way. 2
  4(1)(3)