A1: Ones set; cast, twos lead up. Same, threes lead up.
A2: Twos the same.
B1: Ones go right (man down, woman up): figure eight through this couple.
B2: Ones cross: figure eight through the other couple.
A3: Ones cross and circle with this couple 1½ (12 steps) into lines across (ones in middle, ends improper); ones cross.
A4: Same with other couple; ones cross L (“home”), turn L:
B3: Hey for three with this couple (pass L with opposite sex).
B4: Ones cross: hey with the other couple, finish in middle place.
Originally A1/2 was ones, twos, ones, twos. This version gets the ones naturally into middle place and is a reverse progression (3, 1, 2) so the ones don't have to get to the bottom at the end. See notes at https://colinhume.com/inst3.ht