Friar John who has been sent to give a letter about the plot to Romeo returns to Friar Laurence. Friar John was not able to deliver it. Friar Laurence hopes that Romeo has not heard of the death of Juliet but cannot worry about it. The friar needs to go to the vault and be there when Juliet wakes up.
If the message had gotten to Romeo before his friend did, then Romeo and Juliet would have had a very different ending. This is when the friar finds out that his plan is.....