1–4
: 1c lead down, cross below 3c and cast up into 2plx (2c up)
5–16
: 2c+1c+3c R&L for 3 couples
17–
: 1c set to and turn corners, to finish BtoB in the centre, 1M facing up, 1W facing down
25–
: 1M+2c & 1W+3c Circle3 L (at end 1c pull Rsh back to face P) ; 1c set, petronella to 2pl (2,1,3)