Helen's lace is a beautiful diagonal stitch. It is made up of diagonal stitches that fall on a "true diagonal" over three canvas threads. Every three stitches, the placement of the subsequent stitch changes.
Pay attention to the numbering as it can be tricky. It is beautiful for feathers done in Bella Lusso or Fuzzy Stuff.
The above stitch example was done in Bella Lusso Wool.
You can find a helpful video on Helen's lace below: