It’s a bit of an awkward join that begins with a provisional cast-on of the front-of-leg stitches. The piece needs to be oriented so that the provisional cast-on is at the top of the leg and so that the right side of the front of the leg is aligned with the right side of the back of the leg. The new stitches are joined to the existing back leg stitches at the end of every row — the last front leg stitch is worked together with the first back leg stitch with a ssk (on right-side rows) or p2tog (on wrong-side rows).
There’s a note at the end of page 100 that’s helpful — the needle holding the stitches at the beginning of RS rows is the left back needle; the needle holding the stitches at the end of RS rows is the right back needle.
The instructions don’t mention it, but I cut both yarns at the end of the Back-Leg-and-Heel before working the provisional cast-on for the Front-Leg section. I’m not sure that this was necessary, but it certainly helped me get started in the new direction for the front leg.
Because I’m not good at keeping two circular needles separate for the back leg stitches, I transferred them onto a single longer circular needle and used the magic-loop method. This may or may not be easier for you.
Once I get to the first marker on each back-leg needle, I’ll rejoin for working in rounds and continue to work decreases to shape the gussets.
This sock is a LOT of fun to knit!
Comment on this post to tell me what yarn(s) you’d use to knit these socks to enter a drawing for a FREE copy of New Directions in Sock Knitting, courtesy of my publisher, Interweave Press/F&W Media. I’ll draw a winner Friday morning, April 22.