I've made the edit to show that he uses the ring to draw upon Annatar's power to analyse her better. I'm assuming here that the power of reading people's 'heart's desire' will lead to his appealing to those desires as he wishes to draw people under his influence. He becomes invisible but is still not thoroughly used to these space warp jumps.
Having just posted, I believe it will be someone else who can get the party rolling.
;p