Fire breaks out at a London warehouse and hot on the trail is Jim Bronton, a fire insurance assessor. Reviled by Lloyd's of London as an unethical 'fire engine chaser', his negotiating skills are admired and feared in the underwriting and insurance business. He inspires great loyalty from his assistant Helen Vaughan. Bronton is optimistic that his fortunes will improve and in a fit of generosity, hires Bates, a shady informer currently down on his luck.

Bronton is visited in his office by Stedding, an unscrupulous but clever businessman who wants Bronton to join his gang of arsonists. Bronton turns him down. Later at the race track, Bronton meets a girl, Arden Brent, a former acquaintance. They are attracted to each other and when Bronton is inopportunely summoned back to the office by Bates, he takes her with him.

Back in London, Bates is holding a girl, Polly, hostage. The girl has information about a substantial theft of jewels insured by Lloyds of London, a company founded, coincidentally by Arden's father. Bronton makes a deal with Mr Brent for the return of the jewels in exchange for £2,000. Though Mr Brent is furious, and denounces Bronton as a receiver of stolen goods, he has no choice but to accept Bronton's terms.

Arden and Bronton get married. But Arden has expensive tastes and Bronton has a gambling habit. Very soon he needs money. Remembering Stedding's offer of easy money for small risk he makes the call. He agrees to join Stedding's gang on condition that no lives are put at risk. Bronton is overheard making the deal by Twist, an insurance investigator and the boyfriend of Bronton's assistant, Helen.

The partners at Lloyds of London suspect that a gang is behind the many arson attacks at commercial premises but they have no evidence. Then Twist contacts them with his suspicions of Bronton. The insurers and Twist decide to lay a trap for the gang, a paint shop with high insurance premiums.

Meanwhile the gang are plotting their biggest job, a merchant ship called The Emelda. Stedding conceals from Bronton the fact that there is a high risk of fatalities and when they dynamite the ship many lives are lost. Bronton is devastated. He immediately goes to Stedding and tells him that not only does he want to leave the gang, he wants to confess to the authorities. Arden overhears their argument and in this way learns of her husband's crimes. Stedding taunts her that Bronton only married her to get access to her father. But Arden believes in Bronton and decides to stand by him.

Stedding and the gang decide to set fire to the paint warehouse. The gang find out that Bates has been passing information about them to Twist. They torture him and find out that the paint warehouse is a set up. They lure Twist to the warehouse, beat him and tie him up. Then they start a fire.

Bronton finds out that Twist is in danger. He races to the warehouse which is already on fire. Twist jumps out of the window to safety, but Bronton is knocked back by falling timber and is consumed by the flames.