Major Felix Hagen is a non-canonical character created for the video game Agatha Christie – Hercule Poirot: The First Cases. He is a former British Army officer and a friend of Cassandra Van den Bosch and resident in her house. He is murdered early on in the story and much of the plot revolves around discovering who killed him and why.
In the prologue, a bracelet belonging to Angeline Van den Bosch, Cassandra's daughter, has gone missing. Her mother immediately jumps to the conclusion that Florette Duvall, one of the maids, has taken it. Poirot investigates and proves Florette's innocence. Instead, he finds the bracelet hidden in the chimney of Angeline's room and extracts an admission from her that she had hidden the bracelet herself to prevent her mother from selling it off to settle household financial problems. Angeline hid the bracelet and by claiming it had been stolen, she hoped that perhaps there would be an insurance payout instead. Angeline admitted to this in front of her mother but her mother would not accept it and insists that Poirot take Florette away. Major Hagen joins her in this and tells Poirot and pulls rank, claiming that he knows Poirot's superiors very well.
In the main plot of the game, which takes place many years later, Poirot attends a dinner party organised to celebrate the engagement of Angeline to the wealthy Gedeon Demir. During the dinner, a housemaid Inga Frank discovers that the major has been murdered in his study. Poirot takes up the investigation and soon discovers that all the houseguests alibi one another but they all have a plausible motive as they dislike the major for different reasons.
It soon becomes apparent that uncovering the secrets of the major's distant and recent past would provide the key to understanding why he was killed, and the major had many secrets. Poirot's original purpose as a house guest was to investigate some blackmail letters which Angeline had received. Given the major's blunt and ruthless manner and his love of money, he appears to he the kind of person who would write a blackmail letter (indeed, Cassandra thought so). However Poirot finds that he had also received a blackmail letter but for what and from whom? Comtesse Margaux de Vos dislikes that Major because of the way he moved into Cassandra's house and treats her in a bulllying and boorish manner as well as living off her finances. Why does Cassandra allow this? Archibald Sterling tells Poirot that while the Major tells many stories about his military past, most of these are just stories, best taken with a large grain of salt. There are also others who dislike the Major because of his recent activities working with businessman Ernesto da Silva. What exactly does he do with Ernesto and what has he done to earn him such dislike?