The player takes the role of an Adventurer Archaeologist/treasure hunter exploring a recently-unearthed pyramid in the hope of discovering a stash of valuable artifacts.
The game is mainly remembered for its ending, which received a divided response from the game's audience. Infidel is an experiment in averting the Featureless Protagonist common to interactive fiction: the player character is not just a stand-in for the player, but an actual character with explicitly described goals and personality traits. He's actually quite unpleasant, greedy for fame and fortune, having cheated several people to get his expedition to the pyramid first, and mistreated his subordinates so badly that at the beginning of the game they all pack up and go home, leaving him to press on alone. This plays into the ending, in which the protagonist gets his comeuppance in a way that's dramatically appropriate but, in the experience of some, less satisfactory when considered as a reward for the player who has been encouraged to identify with the protagonist and put in the effort to solve the puzzles and reach the ending.
This game contains examples of:
- Adventurer Archaeologist: The protagonist is a deconstruction. As the author of the game, Mike Berlyn, once put it, the protagonist is his answer to the question, "What kind of a human being would even WANT to ransack a national shrine like a pyramid?"
- All There in the Manual: The game came bundled with a copy of the protagonist's diary, which detailed how he came to learn of the pyramid and the progress of the expedition up to the point where the game opens, and gave a clearer picture of his personality than the game itself mostly manages.
- Bittersweet Ending: The protagonist finds the burial chamber full of treasure, but it's protected by a booby trap that collapses the entrance, leaving him trapped with nothing to do but wait for the air to run out and ponder the life choices that brought him here with no hope of rescue.
- Blaming the Railroaded Player Character: At the end of the game, the protagonist is left thinking about the things he should have done differently. Because of the interactive fiction format, these are all expressed in the form "If only you'd done X". All of them are decisions the protagonist made in the backstory before the game began, so they're not things 'you' the player did or had any choice about doing.
- Diabolus ex Machina: The event that gives the protagonist his comeuppance at the end is of a type that might be generally expected from the genre and the story so far, but the specific instance has no foreshadowing and is impossible to avoid.
- Featureless Protagonist: Unlike very nearly every other Infocom player character, this guy is explicitly depicted as white and male on the packaging. Word of God's intention is that this be a critical deconstruction of the Adventurer Archaeologist and how badly they screwed things up in real life.
- Karmic Death: The protagonist discovers the Queen's treasure, but opening her sarcophagus triggers a booby trap that imprisons him in the burial chamber; the tomb he intended to rob will now be his own tomb. As an extra dose of karma, it's noted that it might have been possible to dig him out in time if there had been anybody who knew where he was and wanted to rescue him, which there isn't because he's already driven everyone away by his own earlier actions.
- Loser Protagonist: The backstory establishes the player character as a greedy opportunist who is not half as clever as he thinks. His situation at the beginning of the game is the direct result of some Jerkass behavior on his part and failure to see what was coming next.
- No Antagonist: You have the "hero," you have a dangerous environment that the "hero" is exploring, and that's it. There are no other characters and no one for the hero to blame but himself.
- Shout-Out: One of the feelies is a letter from the protagonist, whose writing degenerates while he gets drunk on drugged kumiss and spouts out non sequiturs and references to T. S. Eliot, "America the Beautiful", "I've Been Working on the Railroad", Days of Our Lives, Three Little Pigs, Pig Latin, "This Little Piggy", "Home on the Range" (Kansas' state song), The Wizard of Oz, "Home is where the heart is", "Mack the Knife", "Head for the hills", and The Sound of Music.
- Slipping a Mickey: Judging by the protagonist's journal and letter (the feelies) and Abdul's farewell letter, one of his men borrows a calfskin of kumiss, slips a sleeping drug into the drink, and makes him drink it in order to put him to sleep, so they can steal almost all his possessions in retaliation for bossing his men around, treating them cruelly, and making them work on a holy day of rest or obligation.
- Villain Protagonist: The protagonist is greedy, dishonest, incompetent, and a bad boss.