Ep 1. Shadow of Atlantis Part One

In "Shadow of Atlantis Part One," the fifth season premiere of Marvel's Avengers Assemble, our heroes are confronted with a new threat unlike any they've faced before. When the Avengers receive a distress signal from the middle of the Atlantic Ocean, they set out to investigate, but before they can get there, they are attacked by a mysterious group of underwater soldiers.

As the Avengers try to fight off their attackers, they realize that their weapons and powers are useless against them. They manage to capture one of the soldiers, but before they can interrogate him, he escapes and self-destructs, leaving only a strange symbol behind.

Determined to uncover the source of this new threat, the Avengers travel to Atlantis, where they are greeted by Namor, the king of the underwater kingdom. But Namor is reluctant to help the Avengers, as he believes they are responsible for the attack on his people.

As the Avengers try to convince Namor of their innocence and warn him of the danger they face, they learn that the symbol left by their attackers is actually the mark of a powerful weapon that could destroy the entire world. And they soon discover that the weapon is in the hands of Attuma, an Atlantean warlord who seeks to use it to conquer the surface world.

As the Avengers battle Attuma and his army of sea creatures, they are shocked to learn that he has the help of an unexpected ally: Tiger Shark, a former Avengers foe who has been enhanced with Atlantean technology.

With the help of Namor and the Atlanteans, the Avengers are able to defeat Attuma and Tiger Shark and retrieve the weapon. But their victory is short-lived, as they learn that the weapon was only the first of several scattered across the world, and that they must find and destroy them all before it's too late.

As the episode ends, the Avengers and Namor stand united against this new threat, knowing that their battle has only just begun.