Over an almost seven year period writing the Avengers Roy Thomas just kept improving, pushing boundaries and expanding the scope of what the Avengers could be. Successive writers owe him a huge debt, and as a collection this work from 1971 and 1972 is his finest on the series.

It’s elevated by the use of two exceptional artists with completely different styles. Neal Adams took his influences from graphic illustration and realistic newspaper strips, while Barry Windsor-Smith looked to the ornate painters of the mid-19th century Pre-Raphaelite Brotherhood. Both create some exquisite pages. Smith tends to pack his layouts more, often using smaller panels for brief sequences, seen at its best when the Avengers make their way to England (see sample page). His characters sweat, albeit not very realistically, and in places there’s an extraordinary delicacy for superhero artwork. On the downside he saddles Hawkeye with an appalling costume. Adams prioritises dynamism and action, supplying very few quiet moments, but page after page of illustrations only he could conceive. His highlight is when a shrunken Ant-Man travels within the mechanics and internal protections of the android Vision’s body in order to root out a problem, a sequence plotted by Adams. The remaining artwork by John Buscema (drawing in an approximation of Adams’ style for continuity purposes), and Sal Buscema doesn’t match the two star artists, but by the standards of superhero artwork for the time there’s nothing wrong with their pages.

Some of the dialogue is very much of the era, explaining in a manner no-one would ever speak. “I see you’ve forgotten the roller skates that are part of my arsenal” says Iron Man at one stage, but look past that to the ambition of the plots. In 1971 a nine chapter story was unheard of at Marvel, and perhaps for that reason Thomas splits the Kree-Skrull war into a three issue prologue, then the main event. Before involving themselves with the alien races in space the Avengers must first foil a plot by the Kree on Earth, then extricate themselves from political persecution as a senator modelled on Joe McCarthy targets them for harbouring aliens. It’s depressingly contemporary. Amid this Thomas finishes the plotlines from a cancelled Inhumans series he and Adams worked on, introduces the strange idea of the Scarlet Witch’s attraction to the Vision, provides a tearjerking finale and a succession of inventive twists. He’s notable in fooling us on several occasions with the Skrulls shapeshifting. The manner in which the Avengers triumph is very forced, but it’s consistent with the innovation of the preceding chapters.

That’s followed by later Avenger Ares, then a very different incarnation, fermenting war on Earth. As the finale was the Avengers’ 100th issue Thomas’ plot incorporates everyone who’d been a member of the team by that stage, many of whom hadn’t been seen for several years. It’s a great page turner in which Avenger is set against Avenger, the supposedly dead return, a travelling circus provides novelty, and the Avengers eventually invade Olympus. After a strong science fiction story, the infusion of mythical creatures is a pleasing contrast.

Thomas’ introduction runs to eight pages, and is masterclass in diplomacy as well as being informative. When working on the series he had to balance his editorial responsibilities of ensuring a monthly comic with the inability of a fantastic artist to meet a deadline. His recollection of how Adams wanted to conclude the Kree-Skrull War is eye-opening.

The Kree-Skrull War is also available as an individual collection, but beware some poor reproduction, and in Essential Avengers volume 4. Volume 5 opens with the Olympus story.