In the novel 4.50 from Paddington, Alexander Eastley is the son of Bryan and Edie. He is the grandson of Luther Crackenthorpe. He has fair hair and blue eyes. Like his friend, James Stoddart-West, Alexander's hair is well-brushed, and he has a suspiciously angelic face, and perfect manners. His favourite food is apple meringue, and he is also fond of treacle tart.
Alexander always spends part of his school holidays at Rutherford Hall, where he sleeps in the bedroom above the porch.
James and Alexander set up a clock golf set on the lawn at Rutherford Hall. The numbers are rusty, so they and Lucy Eyelesbarrow go to the Long Barn to look for paint, to paint the numbers. Alexander tells Lucy that the Long Barn is used to house Luther Crackenthorpe's collection of art pieces, which he had purchased abroad and sent home. He also tells her that the Long Barn is sometimes used for events, but is almost never used at that time of year. Lucy later discovers a woman's body in a sarcophagus in the Long Barn.
After the discovery of the body, Alexander and James beg Inspector Bacon to let them see it. They take a great interest in the case, riding their bicycles to the inquest, and searching the grounds of Rutherford Hall for clues. They find a torn envelope addressed to Mrs Martine Crackenthorpe, which they give to Inspector Craddock. This seems to suggest that the dead woman is Martine.
Alexander tells Lucy that his father, Bryan, likes her. He hints strongly that he would like Lucy to marry his father, saying that his father needs a proper home life and someone to look after him, because he always gets involved with the wrong type of women. He tells Lucy that his father is "awfully brave" and good-natured. He also says that he would not mind having a stepmother, if she was a decent sort.
For the last few days of the school holidays, Alexander goes with James to his parents' house.
In BBC's 1987 adaptation of 4.50 from Paddington, the part of Alexander is played by Christopher Haley. His age is younger than that in the original novel. Here he is around eleven.
In NHK's anime adaptation 4:50 from Paddington, the character's name is shortened to "Alex". His age is roughly sixteen, the same as Mabel West, which is closer to that in the original novel. The part of Alex is voiced by Daisuke Sakaguchi. Like in the original, he and his friend James play in part in helping to find the body. They meet Mabel who is practising her golf. They want to fetch a football from "the Leaky Barn" and Mabel goes along with them. After they collect the ball and leave, Mabel remains behind to explore the barn and comes across a sarcophagus with the body inside. Like in the original novel, he persuades the police to let him and James look at the body on the grounds that they might know the victim.