Synopsis
In Avengers Mansion Hank Pym has somewhat illadvisedly fashioned a large jewel for his wife Jan's birthday out of the fragments of Dr Spectrum's Power Prism (broken in Giant-Size Defenders #4). Wasp can't resist taking a peek, and when she touches it the recreated Prism takes over her consciousness (which feels similar to when that same consciousness was siphoned into the robot Jocasta in #162). For some reason this results in an explosion.
Quicksilver rushes to investigate the noise. He drops his guard when he sees Jan, and is felled by a blast from the Prism grasped in her fist. Wonder Man followed him, and is equally-disarmed (despite the fact that Wasp is completely hidden by a simulated Spectrum costume). Simon succumbs to hypnosis, as does the reviving Pietro.
But the Prism has its mind set on a more powerful host even than Wonder Man - Thor whom it fought in Iron Man #66. But 1st it must neutralise Iron Man, the only 1 who knows its weakness to ultraviolet light.
Dr Spectrum finds the Golden Avenger helping set up a solar collector, and approaches him as Wasp. She KO's the unsuspecting hero with a blast of solid light, and then transports him in a force-globe to the Pyms' home in Cresskill. There she imprisons him in a force-cell where she already had Pietro and Simon, hidden in the Pyms' pool. But she now sends that cell flying elsewhere.
Henry Pym has seen what his wife has done, and deduced that she's been possessed by the Power Prism. But Spectrum detects him and attacks. Hank shrinks and brings an army of ants into play. But he's also sent a call for help to Avengers Mansion. The responders are Beast and Captain America, along with Black Panther and Ms Marvel in her new blue uniform with the yellow zigzag.
Spectrum holds her own against them all, until MsM knocks her through a wall to the outside. Where she faces Hawkeye, Scarlet Witch and Vision, who uses uv lamps against her. (Iron Man had of course updated the Avengers' files with this info.)
Hank Pym rushes out and tells the Avengers that they've been beating on his wife, as the unconscious form reverts from Dr Spectrum costume to Wasp. They immediately phone their friend Dr Donald Blake, who hurries there as Thor. The Prism senses his presence, but is confused when Thor disappears before Dr Blake rushes up.
Blake discovers that Jan is in an unwakable trance, and the Prism has grafted itself to her palm. Vision suggests they find a previous victim of the Prism, who might know how to deal with it. Hawkeye suggests they go see Dr Strange, who may know what happened to Spectrum's team the Squadron Sinister after GSDef#4. (It should really be Yellowjacket who thought of that.)
Meanwhile we see that the missing 3 Avengers are in their solid-light cell at the bottom of the Atlantic, where the force-field is filtering in enough oxygen from the seawater to keep them alive but sedated. But that force-field depends on the Prism.
The Avengers fly off (in Black Panther's plane because Henry Gyrich has banned them from using their quinjets?). Dr Strange takes a quick break from teaching magic to Clea to explain that he cast a spell to make the 3 evil Squaddies forget their powers and bad deeds. (The 4th guy Nighthawk had already turned good.) But if they break the spell for 1 of them, the other 2 will snap out of it too.
So the team jet off again to confront all 3 villains. (I presume Strange gave them addresses.) Time for the typical divide into subteams tactic. (I presume BP drops some of them off.)
Black Panther, Ms Marvel and Vision go to tackle Hyperion in his new identity as Mr Kant, manager of the Arnold Columbo Health Spa. By coincidence Thundra is applying for a job there, and she intercedes as the presence of the Avengers obviously distresses him. Her intercession takes the form of punching Carol Danvers through a wall. She has more trouble with Vision, as Panther contents himself with some of the gym clientele.
But by now Hyperion has remembered how his microverse planet was destroyed by an Earth-based atomic bomb test. And also how strong he actually is. A Hulk-type shock-wave sends most everybody flying. Then it's MsM vs Thundra round 2, until they notice that Vision has talked Hyperion down, saying revenge won't bring his people back.
Cap, Hawkeye and the Witch find Whizzer, here called Harvey James, working as an industrial chemist. He too wakes up to his power and eludes the trio with his speed and a smoke bomb. But Cap learned how to 2nd-guess speedsters by practising with Quicksilver when they were in the 'Kooky Quartet', and he KO's him with his shield.
Beast goes alone to face evangelist Billy Roberts and tell him that he was once Dr Spectrum. Roberts takes the news, and the flood of memories, calmly. He explains that a follower found the gem (after it was lost in Iron Man #67) and brought it to him. And the Power Prism took him over (but that's not what the Prism claims happened) (leading to his appearances in Defenders). But he is willing to try to break its control over Wasp.
All 3 teams return with Rev Billy to the Cresskill poolside. He does persuade the Prism to leave Jan's palm, but only so that he can use it again himself as Dr Spectrum. A brief battle ensues while Dr Blake sneaks away and returns as Thor. The Prism immediately forsakes Billy Roberts to claim its real Asgardian target. Thor swipes at it with Mjolnir, but the gem attaches itself to the hammer, and now Thor is its pawn.
Meanwhile in the Atlantic we find that when Roberts took control of the Prism the solid light cell holding 3 Avengers underwater disappeared (as did their Prism-generated hypnotic trance). Iron Man's armour reacted to the sudden inrush of water by sealing itself and circulating oxygen. Which revived Tony Stark, who then flew Quicksilver and Wonder Man to safety. But Pietro has swallowed a lot of water. So invulnerable Simon Williams stays to look after him while Iron Man flies off to join the other Avengers.
He arrives in Cresskill to find Thor has the others unconscious. Shellhead tries the uv-light trick, but the god's body is immune. However the enchantment laid on Mjolnir finally kicks in. The tainted Asgardian is no longer worthy to wield it.
Even without his hammer Thor is a match for IM (even with the help of his nifty roller skates). But he lasts 60 seconds, long enough for Mjolnir to revert to a walking stick, and Thor to Don Blake. And the transformation banishes the Prism's consciousness.
Blake becomes Thor again before the rest wake up (he and Iron Man have known each other's identities since #113). Then they all get to celebrate Jan's birthday.