The Fallen Idol (also known as The Lost Illusion) is a 1948 British mystery thriller film directed by Carol Reed, and starring Ralph Richardson, Bobby Henrey, Michèle Morgan, and Denis O'Dea.

Its plot follows the young son of a diplomat in London, who comes to suspect that his family's butler, whom he idolises, has committed a murder.

The young son of the ambassador of a French-speaking European country, Philippe lives a lonely life at the embassy in Belgrave Square, London.

The butler, Baines, keeps Phillipe entertained by telling stories of his daring adventures in Africa and elsewhere, where he claims to have killed a man in self-defense and vanquished lions.

Determined to see if Julie is in the room, Mrs. Baines steps onto a ledge high above the staircase, to peer over a terrace.

Detective Ames of Scotland Yard arrives to investigate, and observes the three places set for dinner, which casts doubt on Baines's story.

Philippe overheard Baines telling the police his fantastical stories weren't true, and that he's only ever once been abroad - to Ostend.

Upstairs two investigators find a woman's footprint in the spilt soil from a potted plant on the window ledge above the main staircase, which appears to confirms Baines' story.

Philippe, finally convinced that he must tell the truth, tries to explain that the footprint was left in a row he'd had with Mrs. Baines two days earlier.

"[5] In his Film Guide, Leslie Halliwell remarked, "A near perfect piece of small scale cinema built up from clever nuances of acting and cinematic technique.

[6] Dilys Powell observed that, "A short story has become a film which is compact without loss of variety in pace and shape",[6] whilst American, Pauline Kael, was less favourable in her review, "It's too deliberate and hushed to be much fun... you wait an extra beat between the low-key lines of dialogue.

[7][8] According to Kinematograph Weekly the 'biggest winner' at the box office in 1948 Britain was The Best Years of Our Lives with Spring in Park Lane being the best British film and "runners up" being It Always Rains on Sunday, My Brother Jonathan, Road to Rio, Miranda, An Ideal Husband, Naked City, The Red Shoes, Green Dolphin Street, Forever Amber, Life with Father, The Weaker Sex, Oliver Twist, The Fallen Idol and The Winslow Boy.

In 2006, William Arnold wrote "Anyone who needs to be reminded how great the movies used to be should hustle on down to the Varsity this week to catch its new-print revival of the British classic The Fallen Idol."

"[11] Ty Burr wrote "the movie's a lasting pleasure: Reed's incisive direction; Greene's easy yet weighted dialogue; the farseeing deep-focus photography of Georges Perinal; Vincent Korda's luxuriant sets.

Sir Ralph, in one of his very few starring roles in a movie, gives Baines the weary sharpness of a man who's smarter than his social betters yet knows enough never to show it.

It was described as "one of the finest British films about children, about the ways they can be manipulated and betrayed, their loyalties misplaced and their emotions toyed with.