Black Panther has arrived at Avengers Mansion to take his place on the team. He contacted them an hour ago when he landed in the US, but now the building appears deserted. He uses a secret entrance Captain America told him about after they fought the fake Zemo in CA#100. After getting past the defences he finds the Avengers (Goliath, Hawkeye and Wasp) apparently dead.
He is arrested for their murder by SHIELD agent Jasper Sitwell (here on an errand for Tony Stark), who calls the police. As the bodies are removed, Hawkeye's is seen by his lover Natasha, just returned from a vacation.
T'Challa can't convince the police of his innocence. They've never heard of his homeland Wakanda. They can't contact Captain America to verify that Panther is his replacement. And the combination lock to the Avengers' meeting room doesn't respond to the code Cap gave him. Panther lets them take him to jail.
When Cap (just returned from battling the 4th Sleeper in CA#101-102), Iron Man and Thor hear the news they vow to investigate (but obviously not fast enough to turn up before the end of the story).
We now learn that the Avengers were 'killed' by a new baddie the Grim Reaper, who is the brother of Wonder Man. Wonder Man debuted as a villain and died as a hero in #9, and Reaper is out for revenge. For that reason his real target was Goliath and Wasp, because Hawkeye wasn't an Avenger back then. After striking them down with a ray from his scythe, he somewhat magically repaired the damage he did breaking in. Now he waits for the other original Avengers to turn up.
Panther escapes from the police (without really explaining why he let himself be taken prisoner in the first place). He returns to the mansion and finds a back way into the meeting room, where he correctly deduced the real killer was hiding.
T'Challa fights the Reaper, who of course gloatingly reveals the whole of his plan. The Avengers aren't dead, the scythe put them in suspended animation. But they will die in 3 hours unless another blast from the blade reverses the process. Reaper's twisted mind seems to justify his actions. He isn't a murderer like the Avengers. It is the police who will be responsible for their deaths (by keeping them away from his scythe, or by performing autopsies?).
Panther proves immune to Reaper's attack (due to his herb-based powers). Reaper appears to fall on his own blade. Needless to say Panther takes the scythe, breaks into the hospital where the bodies are being held, and revives the Avengers.
Later they discover Reaper faked his own death, and escaped. The 3 Avengers' votes, plus Cap's original recommendation, are enough to grant Panther membership.
T'Challa asks about other Avengers, and Goliath recapitulates recent events. Cap joined Iron Man and Thor in retirement. Hercules went home to Olympus. But the remaining Avengers vow to retrieve Quicksilver and Scarlet Witch from the clutches of Magneto.