In the novel 4.50 from Paddington, Alfred Crackenthorpe was the fourth son of Luther Crackenthorpe and the third surviving son at the time of the events in the book. He was the black sheep of the family and known among the other family members as "Flash Alf". His father said that he had always been a coward and a liar and although He had not actually been to prison, but had been near it, and had been involved in some dubious deals in the past. Alfred was in the Ministry of Supply during the war, but left it abruptly under questionable circumstances. At the time of the novel, Alfred had said he was in "insurance". He lived in a flat in West Hampstead but visited Rutherford Hall according to the family tradition of gathering once a year.
When Inspector Craddock met Alfred, he found his face vaguely familiar. This was because Alfred had been involved in a deal involving tinned food with a man called Dicky Rogers, who was known to the police. Alfred had always been on the outskirts of the racket, with an innocent reason for being involved, and nothing could be proved, but the police were sure that he made a small, steady profit.
Alfred does not provide an alibi for the day of the murder, saying he cannot remember what he was doing. However, Sergeant Leakie provided an alibi for him: Alfred had been involved in some shady business at that time. He had been seen at the "Load of Bricks", a lorry pull-up on the Waddington-Brackhampton Road. Alfred had been with Chick Evans, who was known to be one of the Dicky Rogers gang. Alfred had boarded a bus in the direction of Brackhampton a few minutes later.
William Baker, a ticket collector at Brackhampton station, had clipped the ticket of "one of Miss Crackenthorpe's brothers" on the night of the murder, just before the departure of the eleven-fifty-five train for Paddington. It was not confirmed which brother it was, but the police believed it was Alfred.
Alfred was described as "quite a good-looking man with a thin dark face and eyes set rather too close together". Part way into the novel, Alfred told Lucy Eyelesbarrow that he had fallen for her, and had asked her to marry him. Lucy felt that there was a quality of charm about him, perhaps due to sheer animal magnetism. However Alfred reminded Miss Marple of a disreputable man named Jenkins at the St Mary Mead garage.
Alfred was taken ill, along with the rest of the Crackenthorpe family, after eating a curry. Dr Quimper was called to attend them, and found evidence of arsenic in the curry. Dr Quimper was of the opinion that no one had had enough to cause death. However, Alfred later appeared to have a serious relapse, and died. It was believed that he had been given a second dose of arsenic.
BBC's Miss Marple
In BBC's 1987 adaptation of 4.50 from Paddington, the part of Alfred is played by Robert East. In this adaptation he is also the one who is involved in various shady dealings. As he told Emma, he had an alibi for the time of the murder but he could not give it because all his witnesses are crooks. In this adaptation, Alfred is not killed but he is suffering from a terminal illness which he says Dr Quimper failed to diagnose so that by the time it was finally discovered, it was too late. Miss Marple later surmised that it was possible that Quimper might have deliberately refrained from diagnosing the illness.
ITV's Agatha Christie's Marple
In ITV's 2004 adaptation of 4.50 from Paddington, the part of Alfred is played by Ben Daniels. Like in the original novel, he is also the blacksheep of the family--he describe's his business to Miss Marple as "a bit of this, a bit of that". Considerable detail is given about his shady dealings, at least the most current one. He had a blackmail racket going with his girlfriend Jacqueline Briggs. She would get into love affairs with various notable people (in Brackhampton he says). Jacqueline would meet with her lovers in various hotel rooms whereupon Alfred would burst in playing the part of the offended husband and then demand payment. Unfortunately for him, at the most recent job, Jacqueline had really fallen for her lover, one Councillor Marchant, and had gone off with him. Alfred's concern is that Jacqueline might reveal his modus operandi and his previous victims might sue him.
Like in the original, Alfred declines to give an alibi for the time of the murder. However, in this case, Quimper provides one for him. He had seen Alfred at the "King's Head" inn with "old Terry", a bookie's runner. Obviously Alfred could not admit to this before the police.
In this adaptation, Alfred is the only one in the Crackenthorpes to die during the episode. He dies in the same manner as in the original, but the motive is somewhat different. Here, Miss Marple surmises during the denouement that it is again his penchant for blackmail. He had seen Quimper plant the fake "Martine" clue in the garden and had blackmailed Quimper about it. Lucy Eyesbarrow corroborates this because a short time before he died, he had boasted to her that he would soon be getting "a nice little bit of cash".
NHK's Agatha Christie's Great Detectives Poirot and Marple
In NHK's anime adaptation 4:50 from Paddington, Alfred is killed in the same manner as described in the original novel. Here his occupation is described as an insurer. The police know that he needs money but there is no mention of his shady activities. The voice actor behind the character is not credited.