Thor #413 Jan 1990
"Within Me Dwells a Monster!"
Thor and Hercules visit Dr Strange to learn the secret behind his attacks of weakness;
During their study, Ulik begins to pound on the shield surrounding the Sanctum and Hercules feels another wave of fear;
To fight it, he races after Ulik;
Thor learns that it was Loki who secretly ensorcelled him.
Script by Tom DeFalco (plot and script) and Ron Frenz (plot), pencils by Ron Frenz, inks by Joe Sinnott (finishes)