Shazam! 34 (March/April 1978) features a dramatic shift in the art style, as Alan Weiss and Josef Rubenstein come onto the book, though the E Nelson Bridwell story feels much the same as always.
Chicago is the setting for this story, which begins as an explosion strikes the mobile home Billy Batson and Uncle Dudley are travelling in. Billy changes to Captain Marvel, but shortly after this Captain Nazi erects a force field barrier around the city that prevents the magic lightning from striking. Uncle Dudley makes a phone call, and gets urgent news, which prompts him to rush off, though Billy does not discover this until the end of the story.
The suspendium situation does get mentioned in this story. We get a brief recap of Captain Nazi's heydays during World War 2, and his battles with Captain Marvel, Bulletman, Minute Man and Spy Smasher. Captain Nazi had not been seen since 1944, and we learn that he hid out for a while after the war ended. When he learned about the suspendium, he put himself in suspended animation until Captain Marvel and crew came back.
Now Captain Nazi has taken over the building then known as Sears Tower. Billy tries to change to Captain Marvel, but the lightning will not strike. He calls Freddy Freeman and gets Freddy to say Shazam, and the sound of that is enough to activate the transformation. Somehow.
Hearing that Captain Nazi is back, Freddy reflects on how the villain killed his grandfather and crippled him, and how Captain Marvel brought Freddy to Shazam, which is how he gained his powers.
Freddy changes to Captain Marvel Jr and rushes out to Chicago to take down Captain Nazi. He succeeds so well that Cap has to stop Freddy from killing his foe.
The story ends as we see that the lightning repelled by the force field returned to the Rock of Eternity, where it hit and shattered the chains keeping King Kull captive, ever since his defeat at the end of the Justice League/Justice Society crossover a couple of years earlier.
As for Captain Nazi, he returns later in the year in the Shazam series in World's Finest Comics.