Sergeant Ian MacArthur was a police officer who appeared whenever the police were required.
In January 1981, Sergeant MacArthur informed Richard Anstey and Joe Sugden that they had arrested Tom Merrick and Derek Warner for stealing trees from Home Farm last month. Sergeant MacArthur also caught the Beckindale burgular in April 1981, who had burgled multiple houses in Beckindale.
In April 1983, Sergeant MacArthur was called to Emmerdale Farm when a brutal fight broke out between Jack Sugden and a group of rustlers. During the fight, Jack whacked one of the rustlers in the head with a rock, knocking him unconscious. He then visited Matt Skilbeck in December 1983, telling him that Harry Mowlam has made a formal complaint against him about Matt taking Mowlam's dog. Matt told Sergeant MacArthur that he was not going to give Mowlam's dog back.
Sergeant MacArthur visited Mowlam in January 1984 when Mowlam tried to mow down Jackie Merrick. He told Mowlam that he might overlook the charges if Mowlam drops the case against Matt. He also hinted that he knew of dodgy dealings done by Mowlam, and Mowlam backs down and drops the case against Matt. He investigated the shooting of Caroline Bates's dog in May 1984, and Caroline was determined to take Jackie to court. However, Alan Turner managed to put things right and got Caroline to drop the case.
In April 1985, Sergeant MacArthur investigated what caused the accident between Alan and Jackie, when Alan accidentally knocked Jackie off his motorbike. Sergeant MacArthur concluded that it was an unintentional accident and made no arrests. Sergeant MacArthur investigated an armed robbery on a security van in October 1985, witnessed by Sandie Merrick. Sandie was unable to identify the men but Sergeant MacArthur thought he knew who might be the culprit.
Sergeant MacArthur investigated the death of Harry in January 1986. Matt told the police that he might have killed Harry as he accidentally pushed Harry down a bank during a fight the day before. Sergeant MacArthur arrested Matt and later charged him, but Matt was released on bail pending further investigation. Matt then found evidence which cleared him of Mowlam's murder - Harry's body had moved further downstream from where the fight took place, and Matt wouldn't have been strong enough to move Mowlam. Sergeant MacArthur caught Keith Johnson and Derek Warner with the money from the security van and arrested Keith on the scene. Derek got away as he was armed, and Derek took Donald Hinton hostage inside the vicarage. With the building surrounded by armed police, Derek knew he couldn't escape and gave himself up. Ian MacArthur visited Emmerdale Farm in August 1986 and brought Jack some sad news - his wife Pat had died in a car accident.
Sergeant MacArthur was apart of the search time who looked for Jackie when he went missing in March 1987. He then investigated potential dodgy antique dealings, reported by Sandie. Sergeant MacArthur was stationed at Pencross Fell due to the violent protests by the villagers. During one of the protests, Sergeant MacArthur arrested Jackie and Kathy Bates. He also investigated the death of Mr Metcalfe when he was found dead in Crossgil Farm in November 1987. It was revealed to be natural causes.