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

1-8
: 1s & 4s petronella turn into centre (2s & 3s step down/up slightly), all
  set (in diamond formations), 1s+2s also 3s+4s dance RH across
9-16
: 1s+4s dance 1/2 reel of 4 in centre; pass partner RSh & curve to right
  to turn Lady/Man on side 2H to end BtoB facing opp sides (4s between
  2s & 1s between 3s)
17-20
: 4s+2s also 1s+3s dance 1/2 reels of 4 across
21-24
: 2s & 3s dance in (passing 4s/1s) RSh, pass partner RSh to end in 1st/3rd
  place of a square set, 2s facing down, 3s facing up, Lady on Man's
  Left, **while**

: 1s & 4s dance out to sides - 1M+4L to 2nd place, 4M+1L to 4th place
  (Lady on Man's Right). All set NHJ with "new partners"
25-32
: All advance 1 step, pivot right about on spot & chase clockwise (2
  bars), flowing into 8H round 1/2 way into longwise set (4 bars)
  2.4(1)(3)