Fear to tread… With their core directive restored, the Asurans have begun to attack the Wraith on multiple fronts. Under the command of Colonel Abraham Ellis, the Apollo is dispatched to observe the battlefront, but Ellis's orders not to intervene are quickly breached when an Ancient ship drops out of hyperspace.
Inside is Angelus, fleeing the destruction of a world he has spent millennia protecting from the Wraith. Charming and likable, Angelus quickly connects with each member of the Atlantis team in a unique way and, more than that, offers them a weapon that could put an end to their war with both the Wraith and the Asurans.
But all is not what it seems, and even Angelus is unaware of his true nature - a nature that threatens the very survival of Atlantis itself...
The events depicted in this adventure take place during season four of Stargate Atlantis.
Ultimately it turns out that Angelus is a construct created by a creature known as the Hybrid (a living biomass that's part Replicator, part disease) to infiltrate Atlantis. The hybrid was a weapon created by the Asurans as part of an arms race in their war with the Wraith. It was meant to turn their enemies into Replicators, thus eliminating them and adding to their own army. The hybrid proved to be ravenously hungry for power and the Asurans tried to destroy it, but failed. The hybrid ends up mostly on Atlantis with a bit of itself on the Apollo causing damage there. The hybrid absorbs Angelus and does damage to Atlantis despite all attempts to destroy it. Sheppard tries to take it out by ramming it with a Jumper, but only succeeds in stunning it temporarily and ends up inside it. Angelus, whose mind survived being absorbed, manages to take some control of the hybrid's abilities while it's knocked out and works with Sheppard to kill it. Using Sheppard's blood and ATA gene and the hybrid's ability to manufacture what it needs, Angelus creates a poison that will kill the hybrid. Sheppard escapes with Angelus' help just before the hybrid wakes up and retakes full control. The poison works and the hybrid slowly dies over a period of several days and dissolves into M35-117's ocean.
On the Apollo, the crew manages to injure the piece of the hybrid that's there and blows it out the bomb bay doors into a planet's atmosphere which destroys it. After successfully evading three Wraith Cruisers, the Apollo heads to the facility where the hybrid was created to destroy the place. They are joined by a Replicator warship commanded by Oberoth himself, and the two sides call a temporary truce as they both have the same goal in mind. The Apollo and the Replicator warship work together to destroy the facility and then return home, each side leaving the other alone once the facility is gone as part of the truce negotiated by Ellis between himself and Oberoth.
An extract from chapter 1:
Out in the lightless gulfs of space, two great powers coiled around each other like monstrous serpents. And, like monsters, they fought and tore.
A week before, Ellis had watched the blood of the two serpents spread across Colonel Carter’s starmap in a series of vivid splashes: a brilliant, icy blue for the Wraith, a gory scarlet for the Asurans. Each splash, Carter had told him, was the site of a known engagement. Between these battle markers lay the serpents themselves, twisting wildly through each other in three dimensions — an approximation of the two powers’ battle lines.
The whole map, in fact, was an approximation, and therein lay the danger of it. “Most of this information is days old,” Carter had told him, pointing vaguely at a cluster of splashes. “At best we find out about one of these engagements a few hours after it’s over and done. Really, we’ve got no idea exactly where the fighting is going on.”
Ellis had peered closely at the map, a gnawing feeling of worry under his sternum. Carter had scaled the display to take in dozens of star systems, and already half of them were enveloped by the serpents and their terrible wounds. “Is there anything you can be certain of?”
“Just this.” Carter had touched a control, and a small green dot had blinked into life in the centre of the display.
“Let me guess.” Ellis straightened up. “Atlantis.”