A miner named Warner complains about being docked $60. His foreman, Johnson, sneers, saying that he didn't earn it. Later, Johnson enters the mine's toolroom, notices that the methane has reached dangerous levels, and discovers the door won't open. As five miners descend in an elevator, Johnson tries to hammer his way out, creating a spark - and an explosion that travels up the shaft, killing the miners.
At the Lightman Group, mining executive Wallace hires Cal to disprove a coming MSHA report that blames the accident on the company instead of human error. But Wallace doesn't even recognize the faces of the dead miners.
Meanwhile, Gillian meets FBI honcho Dillon in the lobby and reminds him that the Lightman Group is no longer on retainer. Dillon shows her video of Cal playing poker with criminals and threatens Cal with felony charges unless he helps apprehend them. Gillian says she'll handle it and tells Cal to disappear.
Cal and an assistant foreman attend the funeral service for the miners. Checking out the surviving members of the crew, Cal notices that Warner is already drunk, Hoodak is angry, and Darrell is contemptuous. And when another miner, Sully, eulogizes the foreman Johnson, Cal knows that he's lying.
Afterward at the miners' bar, Warner's fiancee, Connie - whose cousin was a "canary" responsible for checking methane levels and who died in the accident - tells Wallace he's not welcome there. When the miners attack, Cal attempts to defend himself with a broken beer bottle until Eli enters, smashing glassware with a baseball bat and telling everyone that the sheriff's outside.
Eli tells Cal it was his idea to follow him, and Cal orders everyone but the four miners out. Meanwhile, Gillian tells Dillon that she'll help him arrest all the poker players (one of whom ordered seven murders, including that of a federal judge) - except Cal.
Back at the bar, Cal questions the shame-ridden Warner, then Connie, while Wallace tells Darrell and Hoodak to leave because their shift is starting.
Gillian and Ria interrogate one of the poker players, who identifies Cal as "Jimmy the Mouth" and a player, known as "Wheels," as the one who invited him.
Meanwhile, Cal goes down into the mine as the new "canary," learns Hoodak stayed aboveground, and tells Wallace that Connie knows what really happened because Warner told her. Cal asks Wallace to turn off the fans and let the methane rise to dangerous levels - but get them out in an hour.
Meanwhile, Hoodak returns to the bar, where Eli pickpockets an assistant foreman and finds a sawed-off door handle - which he concealed from the safety inspectors - and hands it to Wallace. The assistant foreman explains that the crew locked in Johnson as a prank, but when Johnson noticed the methane build-up, he panicked - because he knew he'd turned off the fans to save money. Eli says to tell this the sheriff.
Cal again questions Warner - who still claims the company killed Johnson - then Darrell, then Sully. They think Warner talked. Cal says no. When they notice that the methane has now risen to dangerous levels, Cal whips out a lighter and threatens to create a spark. They knock it away, so Cal grabs a shovel and repeats the threat.
Warner admits that Sully and Hoodak cut the door handle but insist Johnson's death was an accident. Cal realizes that Warner's shame stems from not wanting to believe the crew could kill someone - and Warner's confiding in Connie has endangered her life.
Dillon and Gillian interrogate "Wheels," so named because his failure to pay gambling debts earned him two shots to the spine that left him alive but confined to a wheelchair. Wheels says that he met "Jimmy the Mouth" (a.k.a. Cal) in a subway - somehow he knew Wheels was going to commit suicide by jumping in front of a train - but talked him out of it.
Gillian orders Dillon out, and Wheels admits that "Jimmy" offered to get him out of debt by winning money in the poker game. Wheels then gives Gillian the address where the next game will be held, and she gives it to Dillon - on the condition that if he arrests Hinch, he'll lay off the Lightman Group forever.
Back at the bar, Hoodak pulls a gun on Connie. Eli levels him with a pool cue. Connie grabs the gun and runs. Hoodak follows.
When the mine's fans come back on, Darrell threatens Cal and Warner with a sledgehammer. Cal talks him out of using it. Then Sully pulls a knife - and Warner K.O.'s him.
Cal and Warner return to the bar, where Eli reports that Connie's gone. Cal and Warner find her holding the gun to Wallace, who admits that he pressured Johnson into cutting corners. Cal gets Wallace to agree that the company will accept blame for the accident and pay all damages. Connie drops the gun.
Back at the Lightman Group office, Gillian and Ria celebrate Gillian's saving Cal from the FBI by drinking his 50-year-old, single-malt scotch. Later, Cal shows up at the darkened office - still wearing his miner's lamp hat - and discovers Ria's passed out on a couch and Gillian's extremely drunk.
Cal tells Gillian that Eli earned his stripes. Gillian tells Cal that his FBI troubles are over and she'll stand here until Cal thanks her, which - after a hug - he eventually does. Gillian switches off the light on his miner's hat - and they get close . .