Boswell Marsh, a large bearded man with a brusque manner and brandishing a menacing walking stick, goes to a ticketing agency in London to get three seats for a West End show. While there he phones the Rynox Company, asking for its director, Francis Xavier Benedik. Seemingly enraged when he finds that FX isn't there, he leaves an angry message in which he calls him a crook.
At the Rynox offices, Benedik's secretary tells him that Marsh has now called three times, in addition to several threatening letters in which he claims to have rights to their synthetic rubber process. Benedik waves her worries aside, and those of Sam Rickworth, one of the company's partners and father of Peter (Petronella), who is engaged to Benedik's son Anthony. Sam is worried by Benedik's decision to put all of Rynox's finances behind the Paramata Synthetic Rubber Company, especially as they now have many creditors and no orders for this new product.
Benedik tells Woolridge, the company secretary and accountant, that he intends to settle with Marsh by giving him £100. He phones Marsh and, while making arrangements to meet him the next day, he is joined by Anthony and Peter. He acknowledges that the company is on the verge of ruin, but argues that if they can just go ahead for six months, then the company will will prosper. To this end he sends Anthony to Paris to settle an outstanding contract.
The next morning, Benedik is told by his housekeeper that three theatre tickets have anonymously arrived for her and the rest of the staff for a West End show for that evening. Benedik gives them all the night off, and informs his butler that he is expecting a guest at 10 o'clock, after which he can leave.
Peter goes to a shop to buy a hunting rifle for Anthony. Marsh comes in to buy a handgun and begins to shout and violently wave his walking stick. Peter leaves, asking that the bill be put on to Mr Benedik's account. Marsh is visibly angered when he hears the name, and buys a gun.
At 10pm, Marsh arrives at Benedik's house. After hearing the butler leave the house, he draws the gun. Thirty minutes later, shots are heard from the Benedik house. Both a policeman and the butler arrive to find evidence of a struggle, and the murdered body of Benedik leaning against an open windowsill in the drawing room. The butler tells the police that it must have been Marsh.
Two weeks later, the police inform Anthony that they have been unable to find Marsh. Anthony goes to a creditors meeting and is told that Rynox owes £172,000. He informs them that he will be able to meet that in a couple of days as FX had a life insurance policy for £270,000.
Some months later, the Rynox Company is prospering, just as FX predicted. A Captain James comes to the company asking for money. He has a letter that FX wrote to a Rynox representative in Malaya shortly before he died. FX admits that he had been diagnosed with a terminal illness and that he disguised himself as Marsh to create a motive for murder since the insurance company wouldn't pay if they suspected suicide.
In flashback, we see Benedik remove and hide his disguise and burn the false beard. He fires several shots into the walls and turns over some furniture, then attaches the gun he bought as Marsh to a tree that has been bent back so as to lean into the room. When he fires, the gun is yanked away from his hand by the tree springing back into position.
Anthony and Captain James get into a fight over the letter. Anthony wins and James gives the letter back. Anthony gives him £200 as a fee for delivery and informs him that he has sent the insurance company its money back.
