With MC, ch 4.
Row 1 Sc in 2nd ch from hook and in each ch across (3 sc). Ch 1, turn.
Sc in back loop of each sc across. Ch 1, turn. Rep last row until piece measures 8 (10, 12)", slightly stretched. Sl st short ends tog to form circle.
Next rnd Ch 1, sc in each of next 12 (15, 18) sc around.
*Next rnd Ch 1, 1 sc in back loop of each sc around. Join CC, do not cut MC.
Next rnd Work 1 hdc in free front loop of each st around.
Next rnd Hdc in each st around. Fasten off CC. Pick up MC.
Next rnd Working through both last hdc rnd worked and last MC sc rnd worked, work 1 rnd sc.* Rep from * to * once, join CC in last st. Cut MC.
Heel flap (worked back and forth)
With CC, sc across 6 (8, 9) sts. Ch 1, turn.
Next row Sc in each st across. Ch 1, turn. Rep last row for 2 (3, 3)".
With CC, dec 1 sc at beg and end of next 2 rows -- 2 (4, 5) sts. Join MC.
Next rnd (work in rnds hereafter) Work 2 (4, 5) sc across heel flap, 4 (6, 6) sc across side of heel flap (gusset), 6 (7, 9) sc across instep, 4 (6, 6) sc across side of heel flap (gusset), placing markers for beg of rnd and before and after instep sts -- 16 (23, 26) sts. Work around in sc, dec 1 sc before beg of instep st marker and after (on each gusset) until 12 (15, 18) sts rem. (Note For snugger foot, work 1 additional dec rnd.) Remove instep st markers, leaving beg of rnd marker. Cont to work around in sc until 2 (2½, 2 ½)" less than desired length of slipper. Cut MC. Join CC.
Place marker 6 (7, 9) sts after beg of rnd marker. Work 1 rnd sc.
Work in sc, dec 1 st after each marker. Rep dec rnd 2 (3, 4) more times. Work 1 (0, 1) rnd even. Turn Sock inside out and slip stitch top of toe tog. Thread tapestry needle with tail and run through all sts twice to secure. Draw yarn up tightly and weave in end on inside of Slipper. Weave in ends. Make second Sock same.