28 sts/36 rounds = 4 inches in stockinette stitch

SSP: Slip the next 2 sts knitwise, one by one, insert the left needle into the front of the 2 slipped sts from left to right, remove the right needle then insert it into the back of the 2 stitches together from left to right, then complete the stitch as you normally purl.

M1: Use whichever M1 you prefer. If you have trouble creating the M1 increases because of the tightness of the fabric around the twisted stitches, use a backwards-loop CO to add 1 stitch at the specified location, then work that stitch as charted on subsequent rows.

Working the Twists with a cable needle
1/1 RT: Slip next st to cable needle and hold in back of work; k1 tbl, then k1 tbl from cable needle.
1/1 LT: Slip next st to cable needle and hold in front of work; k1 tbl, then k1 tbl from cable needle.
1/1 RPT: Slip next st to cable needle and hold in back of work; k1 tbl, then p1 from cable needle.
1/1 LPT: Slip next st to cable needle and hold in front of work; p1, then k1 tbl from cable needle.
2/1 RT: Slip next st to cable needle and hold in back of work; k2 tbl, then k1 tbl from cable needle.
2/1 LT: Slip next 2 sts to cable needle and hold in front of work; k1 tbl, then k2 tbl from cable needle.
2/1 RPT: Slip next st to cable needle and hold in back of work; k2 tbl, then p1 from cable needle.
2/1 LPT: Slip next 2 sts to cable needle and hold in front of work; p1, then k2 tbl from cable needle.
2/2 RT: Slip next 2 sts to cable needle and hold in back of work; k2 tbl, then k2 tbl from cable needle.

Working the Twists without a cable needle
1/1 LT, 1/1 LPT | Left Traveling Stitch
With the right-hand needle in back of the work, skip the first stitch on the left-hand needle and insert the tip of the needle into the back leg of the second stitch. Drop both of the stitches off of the right-hand needle. The first stitch will fall free. Insert the left needle into the dropped knit stitch, then slide the other stitch back onto the left needle. Knit or purl the first stitch as indicated on the chart, then knit the second stitch through the back loop.

1/1 RT, 1/1 RPT | Right Traveling Stitch
With the right-hand needle in front of the work, skip the first stitch on the left-hand needle and insert the tip of the needle into the second stitch purlwise. Drop both of the stitches off of the right needle. The first stitch will fall free. Insert the left needle into the dropped knit stitch, then slide the other stitch back onto the left needle. Knit the first stitch though the back loop, then knit or purl the second stitch as indicated on the chart.

2/1 LT, 2/1 LPT | Double Left Traveling Stitch
With the right-hand needle in back of the work, skip the first 2 stitches on the left-hand needle and insert the tip of the needle into the back leg of the third stitch. Drop all three of the stitches off of the right-hand needle. The first 2 stitches will fall free. Insert the left needle into the dropped stitch, then slide the other stitches back onto the left needle. Knit or purl the first stitch as indicated on the chart, then knit the second and third stitches through the back loop.

2/1 RT, 2/1 RPT | Double Right Traveling Stitch
With the right-hand needle in front of the work, skip the first stitch on the left-hand needle and insert the tip of the needle into the second and third stitches purlwise. Drop all three of the stitches off of the right needle. The first stitch will fall free. Insert the left needle into the dropped knit stitch, then slide the other stitches back onto the left needle. Knit the first two stitches though the back loop, then knit or purl the third stitch as indicated on the chart.

2/2 RC | Double Right Cross
With the right-hand needle in front of the work, skip the first two stitches on the left-hand needle and insert the tip of the needle into the third and fourth stitches purlwise. Drop all four of the stitches off of the right needle. The first 2 stitches will fall free. Insert the left needle into the dropped knit stitches, then slide the other stitches back onto the left needle. Knit all four stitches through the back loop.

Ribbing round: [K2, p1] around.
Work ribbing as set for 1 inch.

Work as set until round 15 of the chart is complete.

Following round, chart round 16: Work in ribbing as est to 2 sts before first marker, ssp, slip marker, k2, slip marker, p2tog, work to end of round in patts as est (including 2 increases as charted).

Continue working in this fashion following chart A. When working chart rows 20, 24, and 28, work charted increases as written and decreases around marker as per chart round 16.

When all rows of Chart A are complete change to charts B, C, and D in pattern area as follows: Maintaining ribbing as established, work Chart B over first 16 sts of Chart A area, m1 (this is the first stitch of the first row of Chart C), work chart D over last 16 sts of patterned area. 67[73, 79] sts.

Right sock: Work center stitch of gusset panel. The 32[36, 40] sts just worked are the heel sts.

Left sock: Beginning with center stitch of gusset panel, work in pattern across next 32[36, 40] sts for the heel.

Leave the next remaining 35[37, 39] sts on spare needle or holder for instep to be worked later.

Turn so that WS is facing.

Row 1 [WS]: Sl 1, purl across.

Row 2 [RS]: (Sl1 k1) across.

Rep Rows 1 & 2 until 22[22, 24)] rows have been worked on heel flap. Work Row 1 once more.

Heel Turn
Row 1 [RS]: Sl1, k20[23, 26], ssk, turn.

Row 2 [WS]: Sl 1, p10[12, 14], p2tog, turn.

Row 3 [RS]: Sl 1, k10[12, 14], ssk, turn.

Row 4 [WS]: Sl 1, p10[12, 14], p2tog, turn.

Repeat Rows 3 & 4 8[9,10] more times, until 12[14, 16] sts rem in heel. 

Final row [RS]: Sl 1, k11[13, 15].

Foot
From here, the instep sts will continue the patterning as set by the leg. You'll be working Chart B/D, the ribbing and half of Chart C.

With RS facing, pick up and knit 11[11, 12] sts along first edge of heel flap, using slipped sts as a guide.  Work across instep sts in patts as established.  Pick up and knit 11[11, 12] sts along second edge of heel flap, using slipped sts as a guide. Work across heel sts as follows: K2tog, k8[10, 12], ssk. 32[36, 40] sts rem in heel, 67 [73, 79] sts total.

Foot round: K to start of instep; work across instep in patts as est; k to end of round.
Work 2 more rounds even as set, worked Chart C sts as set and continuing Chart B/D patt.

Right sock, shaping round: K to start of instep; work across instep in patt as set to end of Chart C gusset marker, m1, slip marker, work as set to 2 sts before end of instep, ssp; k to end of round.

Left sock, shaping round:  K to start of instep; p2tog, work across instep in patt as set to end of Chart C gusset marker, m1, slip marker, work to  end of instep as set; k to end of round.
Work 3 rounds even.

Repeat the above four rounds, taking increased gusset sts into gusset pattern until only 1 st rems between chart panel and instep.

At this point, patterns end and instep is worked in St st until foot is desired length to toe: 
Next round: Knit.
Work even until foot measures 6[6.75, 7.5] inches or 2.5[2.75, 3] inches short of full foot length.

Rnd 1: Knit to last 3 sts on sole, k2tog, k2, ssk, knit to last 3 sts of instep, k2tog, k2 ssk, knit to end of rnd. 4 sts decreased.
Rnd 2: Knit.
Repeat Rnds 1 & 2 until 32[36, 38] sts rem, then work Rnd 1 only until 8[8, 10] sts rem.

FINISHING
Cut yarn, leaving a 6 inch tail.
Thread tail through all remaining sts, and pull gently to close, then secure tail to inside.

Wash and dry on large sock blockers if desired.