First Light is set in 2015, four years after Infamous 2, and three years before Infamous: Second Son. Abigail Walker, a young Conduit in the D.U.P.'s custody in their prison Curdun Cay, is ordered to give a demonstration of her powers to one Brooke Augustine whom using the powers of another Conduit "generously" supplies holographic foes for Abigail to kill.
Once that is done Abigail is told to tell the events that led up to her arrest. Seven years earlier, Abigail was one of the first of the new Conduits who emerge following The Beast's rampage across the countryside.
Although her parents tried to cope at first they were left with few options after Abigail injured one of her classmates by mistake. Abigail's older brother Brent Walker immediately grabbed Abigail and ran away with her, the pair turned to drug use to cope but Brent eventually got clean, even going as far as to hide Abigail's stash to help her get clean as well. Brent also made Abigail keep the use of her powers to a minimum to avoid suspicion.
For years Brent worked for gangs to acquire enough funds to buy a boat and sneak across the border from Seattle to Canada where the D.U.P.'s authority does not extend to. However, two years ago, at the location where the plot was supposed to be completed, the gang of Russian mobsters known as the Akurans destroyed the boat, took Brent hostage, and almost killed Abigail with a bomb.
Using her powers, Abigail survives and begins looking for Brent. Abigail soon meets Shane, one of Brent's old contacts and a small time drug lord also looking for Brent. Shane takes advantage of Abigail's naivete to use her to win a gang war with the Akurans almost single handily. When they do finally find Brent, Shane takes him hostage and forces Abigail to help him cement his hold on Seattle's drug trade.
Back in the present Augustine theorizes that the new powers Abigail develops may be a reaction to extreme trauma to help her cope. On the condition that she show her all of her powers, Augustine allows Abigail to fight holograms of her "D.U.P. Troops." Once the latest challenges are completed, Abigail continues her story. Another employee of Shane's working for the city's tech support department named Jenny offers to help look for Brent.
Jenny has narrowed down where Shane is keeping Brent to three shipping crates dotted around the city. Finding the crates not only does Abigail discover that Brent isn't in any of them but Shane, already on to them, hunts down and kills Jennifer. Shane has Abigail help him force the police's favor by having Abigail slaughter the police force while he has a sit-down with the chief.
The chief agrees to Shane's terms, on the condition that Abigail leaves Seattle and doesn't come back. With this Shane sends Abigail to pick up her brother. Unfortunately, it turns out to be a trap where Shane attempts to kill Abigail with a homemade gas chamber, Abigail however is able to pull through and escape. Back in the present, realizing that Abigail is still holding out on her, decides to send her to yet another new arena.
Taking inspiration from Eugene's love of the Heaven's Hellfire game Augustine has Abigail fight her now literal Demons. Once the third arena is completed Augustine has Abigail finish the story. The still alive Abigail "negotiates" a new deal with Shane, he hands over Brent, alive and intact, and she stops tearing apart his gang and operation. Shane has Abigail meet him at the Crocodile where he sticks her with a drug filled needle.
In the resulting drug filled haze Abigail accidentally kills Brent, leaving her emotionally distraught and defenseless as the D.U.P. closes in on her. Back in the present Augustine reveals that she knew Abigail's story all along, she has been making her work up the nerve for murder, revealing that she has Shane in custody and offers Abigail the chance to kill him.
Gladly accepting Augustine's offer Abigail's "enthusiasm" leads her to blow a hole in the wall of the prison into the outside world. Though Shane miraculously survives, battered and bruised, he escapes by hijacking an APC with the D.U.P. and the now freed Abigail in hot pursuit. With the D.U.P's unwilling assistance, Abigail catches up to Shane and violently kills him, avenging her brother. Augustine, after she hears that Shane had been executed, she states that Abigail is 'ready'.
Alongside Eugene and another Conduit named Hank Daughtry, Abigail is released into the Military's custody. During the drive, Hank reveals he's smuggled in a bent paper clip to pick their restraints, allowing him to hijack the truck and crash it at Salmon Bay, leading to the events of Second Son.
- Neon Races-Abigail can chase down floating balls of Neon gas and Conduit energy called "lumens" that reward her with skill points to increase her powers.
- Arena Challenges-Both Abigail Walker and Delsin Rowe can fight against hoards of holographic enemies in Arena Challenges inside Curdun Cay. Completing challenges reward the player with Skill points that they can use to upgrade their abilities.
- A New enemy-Exclusive to the arena is a new enemy faction: Demons, with their own unique powers and abilities.
- This game marks the first time in the series where the protagonist is a female.
- This game marks the second time in the series where there is no Karma meter (The first being Infamous: Festival of Blood). This is likely due to the player having to fight police officers rather than simply ignore them, cause chaos in the streets, and how Abigail canonically murders Shane at the end of the campaign and players are not permitted to spare him.
- Due to the game reusing assets from Second Son, many of the launching points Delsin used, such as vents, and, satellite dishes are visible.
- During the recording of the final scene in Curdun Cay, when Augustine sicks Abigail on Shane, Laura Bailey's scream was so loud and forceful, she broke several of Sucker Punch's recording equipment.