Base rnd, each side: Multiple of 3 + 2 + corner sts.
Begin 3 sts to left of corner st.
Rnd 1: Ch 4, 2 dc in first ch of ch-4, skip 2 sts, *[Leaning Tower Stitch in next st, skip 2 sts] to corner st, (Leaning Tower Stitch, ch 1, Leaning Tower Stitch) in corner st, skip 2 sts; rep from * around, join with slip st to 4th ch of ch-4.
Rnds 2–4: Ch 4, 2 dc in first ch of ch-4, *[Leaning Tower Stitch between next two tower-groups] to corner, 2 Leaning Tower Stitches between two corner tower-groups; rep from * around, join with slip st to 4th ch of ch-4. Fasten off.