2/9/15: Updated the PDF with an edit to the instructions to fix the count for row 20!

Clarification requested by someone on the Vault pattern, and I sent her this, which seemed to help:

Think of the 84 stitches in row #21 as a grouping of five stitches, the first stitch has two double crochets in it. The next four stitches contain an X created by one triple crochet crossing backwards over the front of the other.

So in stitch #1: 2 double crochets

Then yarn over twice and insert the hook in the back loop of four stitches later (stitch #5), complete the triple crochet.

Now, yarn over twice again, and double back three stitches to the one right after #1 (stitch #2), and insert hook into back loop, complete the triple crochet.

That completes your 5 stitch pattern. The next stitch will start the stitch pattern over with two double crochets in the same stitch.