Silver Surfer, Vol. 3 #7 (1987)

Triangle!
On Earth, Mantis learns that the six soul gems (later renamed Infinity gems) are critical to the plans of the Elders. They have five of the six already. She is captured by plants loyal to the gardener, and barely manages to send a message out across the cosmos that is heard by Shalla-Bal, but Shalla-Bal believes it to be her imagination. The Silver Surfer has, in the meantime, defended Zenn-La from Kree attack, and traveled to Kree-Lor to deliver his warning to the Supreme Intelligence. The Supreme Intelligence is happy to leave Zenn-La out of the conflict, but refuses to do the same for Earth. In retaliation, it uses the only soul gem not possessed by the Elders to steal the Surfer's soul.
Release Date: 1987