J.K. Rowling has said she is now writing Lethal White (Strike 4) alongside another book under her real name. It is unknown which book will come first. J.K. Rowling mentioned on Twitter in early February that the fourth Strike book is “well underway….”
In an interview shortly after the release of Career of Evil, Rowling revealed that book 4 will pick up right where the third book left off.
In early March 2017, J.K. Rowling replied to a fan on Twitter (@luminousmax405) who asked her what the title is for the fourth Strike book. She used a hangman-like game to give fans a chance to guess the title themselves. She wrote:
“_ _ _ H _ _ _ H _ _ _”
A lot of fans correctly guessed the first word as “Lethal”, a few guessed the second word as “White” but it wasn’t for another 50 minutes that someone put the two together: Lethal White.
Here is a fan made cover of the book by John Ross: