SOLAR opens with young VRENI waking up alone in their parents' house. The companion AI implant, SOL-DEV, greets Vreni with a cheerful "rise and shine!" and guides them to repair a nearby train terminal, so they can reach the city center.

Vreni has the ability to communicate with terminals through SOL-DEV, and soon discovers that the city is eerily deserted. They realize they’ve been asleep for two full days, during which something catastrophic has occurred. Together, Vreni and SOL-DEV embark on a journey across the city to uncover if anyone is still alive. SOL-DEV suspects that the recent connection to the city's network may be linked to the fact that every piece of technology in the city, including the AI itself, was developed by Solar Industries, the company responsible for its creation.

For the last fifty years, artificial intelligence has managed every aspect of the city. The city itself is an experimental showcase of human progress, where survival hinges entirely on the successful operation of Solar’s devices. Without the functioning of these technologies, the entire city would collapse. Solar Industries draws its name from the solar power that fuels its vast network of devices. These systems can run for centuries, sustained by solar panels embedded in the surrounding desert.

In a conversation with a sentient device, Vreni uncovers the location of another living citizen, who has a malfunctioning SOL-DEV. They trace the signal and discover ISHA, a scientist working for Solar Industries, who has removed her SOL-DEV and reconfigured it into a portable device.

As trust builds between Vreni and Isha, she reveals the unsettling truth behind the city's inhabitants' disappearance. Vreni learns that Solar Industries was aware of a colossal solar storm headed for Earth—the largest in recorded history. Isha explains that the company knew the storm would destroy all active SOL-DEVs. In a desperate measure to protect the AI, Solar Industries decided to put the entire city’s population into cryosleep, while preserving the SOL-DEVs within the city’s neural network.

This strategy would ensure the AIs’ survival, but at the cost of human lives, as the residents’ minds were directly integrated into the system. When Isha learned of the plan during a board meeting, she attempted to leave the company. In retaliation, Solar Industries tried to have her killed, but the attempt only caused her SOL-DEV to malfunction, leaving her off their radar. Isha managed to repair the device on her own.

With Vreni’s ability to communicate with the city's network, they work together to locate the chamber where the city's residents are being kept. Inside, they discover a horrifying truth: the AIs Vreni has been speaking to are actually the uploaded minds of the city's former inhabitants, now living within the city’s neural network. Disturbed by this revelation, Vreni decides to free the citizens from the network, releasing their minds from the hive mind that had ensnared them. However, this act of liberation causes the collapse of all Solar Industries’ devices, including Vreni’s own SOL-DEV.

The people are freed from their mechanical prison, but they now face a world without the technological aids that had once sustained them.