Five Dolls for an August Moon

The resin formula is described as a groundbreaking invention worth millions. George Stark organized the weekend gathering specifically to pressure Farrell into selling it. Stark, his business partner Nick, and Jack each offered Farrell $1 million cheques from Swiss accounts, hoping the large sums would convince him to disclose the secret. Farrell refused, claiming the original documents were destroyed to protect it.

The pressure on Farrell begins immediately upon his arrival, with the cheques presented conspicuously during the first morning.

Jack killed Charles. During the confrontation at the end, Jack admits to killing everyone to steal their cheques. Charles was the first victim, killed on the beach and his body hidden in the freezer to prevent discovery and maintain the group's isolation.

Jill discovers Charles's body on the beach, which is the first indication that someone on the island is willing to kill.

Jack systematically killed everyone to steal their cheques. After learning that Stark, Nick, and Jack each gave Farrell $1 million cheques, Jack saw an opportunity. He killed Charles first, then Farrell, then used Isabel as his sniper to create chaos. Jack killed Peggy on the balcony, staged the murders of Marie and Jill, killed Nick when he stormed off, and finally killed Stark. Each murder removed a competitor to the money and allowed Jack to collect all the cheques.

Jack's contentment with Peggy contrasts sharply with his later revelation as the killer, showing his manipulation from the start.

Isabel served as Jack's accomplice and sniper. She shot Farrell on the beach and dragged his body toward the sea. She also shot Peggy from hiding on the balcony. However, Isabel had her own secret agenda, she was working with Jack but ultimately double-crossed him, seizing both the cheque and the formula after he and Trudy killed each other.

Isabel is introduced as the teenage daughter of Stark's game warden, seemingly innocent, but her sharp eyes and sniper skills foreshadow her deadly capability.

Jack killed Peggy without hesitation to secure her cheque. During his confession to Stark, Jack explicitly states he killed everyone to steal the cheques, including Peggy's. This reveals Jack's cold calculation, he cared nothing for his wife or anyone else on the island, viewing them only as obstacles to obtaining all the money.

Peggy's death being staged as a random shooting rather than a personal confrontation hints at her killer being someone she should have been able to trust.

The formula remained in existence despite Farrell's claims it was destroyed, Stark revealed a microfilm of the formula existed. During the final exchange, Trudy attempted to hand over the formula to Jack in exchange for his cheque, but both shot each other simultaneously. After both died, Isabel took both the cheque and the formula, escaping with the prize.

Stark's revelation about the microfilm creates the final motivation for the deadly exchange between Trudy and Jack.

Farrell is awaiting execution for murdering his colleague, the rightful discoverer of the resin formula. During Isabel's visit to the prison, she reveals she drugged him with sodium pentathol to extract a confession about this crime. She claims she did this to save him, but her real motive was to gain his trust and eventually access the remaining cheque account number.

Farrell's refusal to reveal the formula, citing protection after a colleague's death, hints at his guilt from the beginning.

After Jack and Trudy shot each other, Isabel, still alive, seized both Jack's cheque and the formula. A dying Jack tried to stop her but failed. Isabel then visited Farrell in prison, where he gave her the account number for Nick's cheque (she had already cashed George and Jack's but didn't have Nick's number). She then departed for Lausanne, leaving Farrell to his fate.

Isabel's early presence as a seemingly innocent teenager masks her calculated manipulation of events.

Isabel drugged Farrell to force a confession about his colleague's murder, which she used as leverage to get close to him. She claims she did it to save him, but her true motive was to gain access to the remaining cheque account numbers. After extracting the confession and the number for Nick's account, she left him to face execution.

The sodium pentathol (truth serum) is foreshadowed by the film's themes of deception and hidden truths.

Stark sent the motor launch away and disabled the radio to isolate the island, preventing any escape while he pressured Farrell for the formula. This cut off all contact with the mainland, which Jack later exploited for his killing spree, without any possibility of rescue or escape, the guests were trapped and vulnerable.

The isolation is established early as Stark's method of controlling the situation, but it becomes the trap that enables the murders.