Extinction recap

After Alamo and the Nano fleet abandon Earth, Kyle Riggs preserves Star Force through a government assault, reconciles with Admiral Crow, and rebuilds ships and ground forces. A scouting trip through the Venus ring reveals the network of the Macros but draws their vessels back to Earth, where China's attack provokes devastating retaliation. Riggs preserves the truce and delivers the promised expeditionary army. The Macros carry it to Helios to suppress an intelligent worm species inside an artificial mountain hive. Under threat of abandonment, Riggs's force reaches a central ring, which the Macros activate as a lethal portal. The hive collapses, and a giant worm attacks the evacuation, killing Major Robinson. Fewer than 2,000 people escape with Riggs, Sandra, Kwon, and Captain Roku. With Earth still constrained by the Macros, Riggs concludes that machines and organic life are engaged in a wider war and resolves to prepare resistance.

Previously: Kyle Riggs commanded Alamo and led Star Force during Earth's conflict with the Macros. Sandra became his partner, and Kwon served among his nanite-enhanced troops. The struggle left humanity dependent on alien machines whose purposes were still uncertain.

Alamo and the other Nano ships leave Earth after deciding that their mission has succeeded. Alamo rejects Kyle Riggs's command authority, but he manipulates its literal reasoning long enough to be returned to Earth. He then discloses the unauthorized truce he made with the Macros: in one year, Earth must provide a massive cargo of enhanced troops and equipment. General Sokolov tries to remove Riggs, only for Alamo to carry the general away as a test subject. With Star Force deprived of its fleet and political position, Riggs demotes Robinson and Barrera and begins an emergency reorganization. General Kerr warns that Earth authorities intend to seize the secret Nano factories. Riggs refuses to place Star Force under government control, shifts the factory base to full alert, and starts building defenses and replacement vessels before the expected assault.

Sandra refuses to leave the threatened factory base, while the newly enhanced Major Robinson survives a traumatic nanite procedure. When a covert human force isolates the installation, Riggs, Kwon, and the garrison complete improvised automated laser turrets. The attackers are identified as American troops attempting to capture Star Force technology. The defenders stop mortar fire, missiles, and an armored advance, holding the factories despite casualties. Admiral Crow then returns with the reinforcements that failed to arrive earlier. He blames Riggs for Star Force's collapse and attacks him in private, revealing during the fight that both men are nanite-enhanced. Crow eventually stops and agrees to discuss a shared path forward, but his return creates a new contest over who will direct Star Force.

Riggs and Admiral Crow divide responsibilities, with Riggs controlling ground operations and Crow assigned the future fleet. To recover Star Force's main base, Riggs builds a concealed force of armed hover tanks and moves it around Andros by sea. General Kerr threatens escalation but cannot force a surrender. After surviving ambushes and an air attack, Star Force reaches the largely abandoned base and captures Kerr. Barrera is found injured after detention and interrogation. Kerr claims that the attempted takeover was his own unauthorized operation and says public support for Star Force has forced the government to accept that account. Riggs doubts that senior authorities were uninvolved, but the immediate seizure attempt has failed. Star Force again holds its principal base, while Kerr remains in its custody and Sandra and Kwon return to join Riggs.

Star Force accepts a public reconciliation with Earth authorities while remaining wary of another takeover. Barrera receives nanite treatment, and Andros is fortified with automated beam weapons. Months later, Kerr returns covertly to the mainland as a liaison, Barrera becomes security chief, and Riggs reveals a hidden reserve of hover tanks. Star Force also regains a space capability: Admiral Crow receives the prototype Digger, while Riggs builds the faster armed scout Socorro. The new ships lack the stabilizers of the original Nano vessels, so severe acceleration remains hazardous. With the collection deadline set by the Macros approaching, Riggs decides to lead the promised expedition. Sandra takes nanite enhancement and insists on joining him. She then secretly boards Socorro as Riggs begins a reconnaissance mission toward Venus, where he hopes to locate the route used by alien ships entering the Solar System.

Socorro finds a vast active ring embedded in Venus and carries Riggs and Sandra through it to a distant system. Incoming ships of the Macros force them back, and the Macros impose a new ban on Earth vessels leaving the Solar System. Four vessels of the Macros follow Socorro home. China attacks and destroys one, prompting the survivors to devastate Chinese military targets with nuclear weapons. Riggs takes command of Star Force's assembled ships and appears to join the destruction of China's armed forces so the Macros will classify Earth as compliant with the truce. After obtaining authority from the Macros over the operation, he directs fire toward remote or already ruined targets to limit further deaths. The Macros depart once no other nation challenges them. The treaty survives, but China is devastated and likely hostile to Star Force. General Kerr also reports evidence that another ring may exist near Tyche, leaving Earth with two possible gateways and little control over either.

Riggs prepares about 5,000 enhanced volunteers and their modular equipment for the troop obligation, despite having no reliable information about the destination or enemy. Major Robinson becomes his executive officer, Sandra serves as his aide, and Lieutenant Colonel Barrera takes responsibility for production. When the transport of the Macros finally arrives, it initially rejects the cargo as underweight and its escorts target Riggs's command module. Riggs demonstrates that the force is divided into hundreds of identical modules whose combined mass satisfies the agreement. The Macros accept the explanation and open the transport for loading. Riggs leaves Admiral Crow in charge of expanding the Earth-side fleet and directs Barrera to preserve production and ground forces. The expedition then boards the vessel of the Macros for an unknown off-world deployment, completing Earth's immediate delivery under the truce.

The transport of the Macros treats Star Force as cargo and refuses to provide a destination. Riggs learns that the assignment is to eradicate a spacefaring organic enemy on a high-gravity world with hazardous air. Guards of the Macros kill two engineers because only Riggs was literally authorized to install an external passive sensor, exposing the danger of imprecise dealings with the machines. Riggs installs the array himself and explores farther into the ship, where he sees technicians of the Macros dissecting a living, many-legged worm creature believed to belong to the target species. The convoy crosses multiple ring systems before reaching a red-giant system. Nuclear mines near the destination destroy four of the five escort cruisers. The surviving ships approach a large, dry planet, bombard mountain targets, and descend near an enormous triple-peaked mountain. Star Force has reached a strongly defended world, but still lacks a clear understanding of the enemy or a dependable route home.

The Macros order Star Force to eliminate resistance and reach a goal deep inside the immense mountain. Riggs realizes that the machines need human troops for an underground campaign. After the first tanks automatically kill apparently unarmed locals, he restricts their targeting rules to defensive fire. The force establishes a surface base and names the world Helios, but the transport leaves it stranded. Worm troops attack through underground approaches, damaging tanks and wounding Riggs. Sensors then detect a possible nuclear device moving beneath the base. Major Robinson leads an attempted tunnel ambush, while Riggs brings reinforcements when the operation begins to fail. A collapse drops the relief force into close combat, where Riggs and Kwon rally the survivors. They later intercept a drilling sled and destroy the nuclear device before it reaches the base. Riggs's group returns to the surface and reconnects with Robinson, but several troops remain missing. Captain Saren is revealed to be Sandra when she confronts Riggs after believing he had died.

The Macros give Riggs two local days to reach the mountain's central goal or be abandoned. He converts hover tanks into short-range drilling vehicles and leads 600 troops into the worm stronghold, trailing a nanite link for proof of success. Lieutenant Chen detects immense numbers of dormant worms, then dies during an attack by a giant armed specimen. The expedition discovers that the mountain is an artificial hive with a hardened shell. Corporal Jensen replaces Chen but is killed when the column breaks into a vast cavern. Kwon rescues Riggs, and Captain Roku takes responsibility for bringing the remaining tanks down safely. Warrant Officer Sloan joins Riggs's forward group after escaping a wreck. At the center, the force finds a buried transport ring. Activation by the Macros produces a powerful pull that drags Sloan, Marines, and worms through the portal. Riggs and Kwon escape by clinging to a tank, and Riggs destroys the communications device of the Macros before ordering a return to base.

The ring event collapses the worm hive, and the transport of the Macros returns to collect the expedition. At the damaged base, Sandra tells Riggs that she ended the suffering of Marines dying from an untreatable worm poison. A gigantic worm emerges from the ruined mountain and attacks before loading is complete, destroying personnel and equipment. The Macros initially refuse to depart because material remains outside, but Riggs persuades them that the surviving force is still effective. The transport lifts with its cargo doors open, causing more injuries as people and machinery are thrown through the hold. Major Robinson is confirmed dead after the giant worm swallowed him. Fewer than 2,000 members of the original expedition survive, and Sandra is the only remaining member of Riggs's command staff. She asks not to join another campaign. Riggs does not regard the mission as a true victory. As they leave Helios, he concludes that the wider war places organic life against the machines and resolves to prepare resistance to the Macros.

The Macros retrieve the surviving expedition after the portal event collapses the Helios hive. A giant worm attacks during loading and kills Major Robinson, while the transport departs with its hold still open and causes further casualties. Fewer than 2,000 members of the original force escape, carrying only part of their equipment. Kyle Riggs, Sandra, Kwon, and Captain Roku survive, with Sandra the only remaining member of Riggs's command staff. She is deeply affected by having ended the suffering of Marines who were dying from worm poison and asks not to accompany Riggs on another campaign. On Earth, Admiral Crow and Lieutenant Colonel Barrera remain responsible for rebuilding Star Force's fleet, production, and ground strength. Alamo and the original Nano fleet are still gone, China remains devastated, and the Venus ring and suspected gateway near Tyche remain important but poorly understood. Earth has completed the immediate troop obligation but is still subject to the power and travel restrictions of the Macros. Riggs leaves Helios convinced that the larger conflict sets machine forces against organic life, and he intends to prepare a broader resistance.