{{explanation}}
3s & 4s start on opposite sides 1,2,(3),(4)

1–4 
: 1s+4s xRH, cast down/up, 2s step up, 3s down
5–8 
: 1s+4s turn RH to prom hold, btob, 1s up, 4s down (W on M's left)
9–16
: 1s with 2s, 4s with 3s, Rsh R3 across
17–20 
: 1W/2M, 4W/3M turn LH, 1M/2W, 4M/3W turn RH
21–24 
: 1s x up, cast dn as 4s x dn, cast up 2,1,(4),(3)
25–32
: All set, 1s/4s petronella twice in tandem, all set 2,4,(1),(3)