Crack between brick backed plaster and plasterboard backed plaster

I have a room where there is a large crack running from floor to ceiling along one of the walls. To the left of the crack it sounds solid and appears to be plastered onto the side of the chimney, to the right it sounds hollow and I believe it a stud wall with plasterboard.

Both sides seem very solid with no detectable movement in them. What is the best way to repair this crack?