Dave is correct.
step 1. use the split poly tool to add verts to the lone edge (if you click and then drop the tool you'll leave a floating vert)
step 2. use the merge vert tool to merge the vert of the other surface to the verts you just created. (you'll find this tool under edit mesh. It allows you to drag one vert to another and merge them.)
"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675