'Anonymous' has been in touch again. Thanks to those who worked out his first message. Obviously, I am terrified. This is their second email:
You'll never find out who I am. I live off the grid.
You don't need me to point out the clue there - Sherlock
SHERLOCK I AM COMING TO GET YOU
This is a form of grid cipher. There are 25 letters in the message so it's easy to work out the factors - 5 x 5! Create a 5 x 5 grid and write the letters in the grid from left to right, top to bottom. The decoded message reads down from top to bottom, left to right!