Cast on 92 sts using the off-white yarn and divide them onto four needles, 23 sts each. The beginning of the round is between needles I and IV. Work 12 rounds of ribbing. Knit 1 round, increasing 1 st on needle IV = 93 sts.

Begin the colourwork from row 1 of chart I and work the 93 st pattern. Then work rows 2-66 of chart I and rows 67-132 of chart II.

1 st decreased at the beginning and end of rows 23, 34, 46, 58, 71, 81, 89, 96, 103, 111 and 121. 1 st decreased at the beginning of row 132. 70 sts on the needles after the decreases. Redistribute the sts: 18 sts each on needles I and IV, 17 sts each on needles II and III.

After row 132, begin the heel flap: using the off-white yarn, knit the sts on needle I onto needle IV = 36 sts. Leave the other sts on hold and turn work. Purl to end of row and at the same time evenly decrease 2 sts = 34 sts.

Begin the reinforced stitch pattern:

Row 1: (RS) *Slip 1 with yarn in back, k1*, repeat *-* to end of row. Turn work.

Row 2: (WS) Slip 1 with yarn in back, purl to end of row. Turn work.

Repeat rows 1-2 a total of 16 times = 32 rows.

Continue the reinforced st pattern as established and begin turning the heel: work the sts from the right end of the heel flap until 12 sts remain at the other end. Work the skp decrease (= slip 1 knitwise, knit 1, pass the slipped st over) and turn work. Slip 1, p10, p2tog, turn work. Slip 1, work until 11 sts remain, skp. Continue in the same manner, decreasing sts on the sides with 12 sts in the middle. When only the middle sts remain, distribute them onto two needles, 6 sts each. K6 to move the yarn between needles IV and I.

Using needle I, pick up 16 sts from the left edge of the heel flap + 1 st from between the needles. Move the st you picked up from between the needles onto needle II. Using needle IV, pick up 16 sts from the other edge of the heel flap + 1 st from between the needles. 80 sts on the needles.

Continue the colourwork from row 1 of chart III and knit the picked-up sts through the back loop. Work rows 1-13 of the chart. Work the gusset decreases following the chart at the end of needle I and beginning of needle IV. 68 sts on the needles after the decreases.

Continue the colourwork from row 14 of chart III. Work rows 14-48.

Use the off-white yarn for the rest of the sock. Begin the toe decreases: k2tog, k1 at the end of needles I and III, and k1, skp at the beginning of needles II and IV. Work the decreases as established on every 2nd round until 12 sts remain on each needle. Then work the decreases on every round.

When 12 sts remain, break the yarn and pass it through the sts. Securely weave in the ends.

Knit the other sock to match.

Finishing

Steam the socks lightly.