The unnamed hero must find the way through an abandoned house in order to rescue a sibling. The quest involves magic and solving logic puzzles while discovering sinister secrets of the house's former inhabitants.

The player regains consciousness from a car crash in front of a large, old mansion. The player's sibling (a younger brother in the computer version but an older sister in the NES version) is gone, and the car is soon lost, as it bursts into flames. The only option is to enter the mansion looking for your sibling, and for help.

The main house consists of two floors and a tower, most parts being in early 20th century style. Some rooms (e.g. the servant's bedroom) have newer decoration, suggesting that a younger person lived in that particular place. No help is to be found, as there is not a single living soul inhabiting the house. It is not long before the player is greeted by the first undead dweller, however.

It gradually becomes evident that the house once belonged to a sorcerer with a number of apprentices. Dracan, the most talented apprentice, became corrupt and killed the other inhabitants with his magic, resulting in the house becoming haunted.

Aside from the house, there are three backyard buildings to explore: the observatory, where some of the final events take place; the greenhouse, which is not as infertile as it first seems; and the chapel, which leads into a cemetery maze. Several places are guarded by magical creatures, including apparitions, hellhounds, and zombies, as well as some more unconventional entities; one is a tiny demon that flies by periodically, holding a key.

The quest to rescue the player's sibling is mostly a matter of gaining access to the locked-up or guarded parts of the estate. As in the other MacVenture games, there is a time limit; in this case, the evil presence of the mansion gradually takes control, and the player may eventually end up as a zombie. This element is partially absent from the NES version, as it is instead caused by a useless item that may be avoided. Since the story largely revolves around magic, many of the game's puzzles seem illogical. Hints for these and bits of the background story are unraveled in the various diaries and scrolls found within the grounds. Still, because the gameplay is very non-linear, the ending is somewhat abrupt.

As with the other NES MacVenture games, Uninvited now had music and elements of the written narration and storyline were altered, including these:

• In the NES version, if the player uses the phonograph in the Game room (Rec room in original versions), you'll hear a broken-record version of the main theme from Shadowgate, another NES-ported game in the MacVenture series. (A similar gag appears in another point-and-click game, Maniac Mansion.)
• As mentioned above, the sibling trapped in the mansion is changed from a younger brother to an older sister in the NES version.
• In the NES version, the player does not have a time limit unless it picks up the ruby in one of the bedrooms. Even then, the player can drop the ruby and the time limit is terminated.
• As with the other NES ports, the game texts were severely simplified, in some cases also adding hints or elucidations for the gameplay. As an example, a hallway picture reads as follows in the NES version: It's a small, (sic) painting of a young fellow.
• In the original game, the address was, "Master Crowley, 666 Blackwell Road, Loch Ness, Scotland". However, at the time the game was released, Nintendo had stringent policy necessitating the removal of any remotely offensive material. Rather than create a new address, it was simply shortened to "Master Crowley". This is likely a reference to occultist Aleister Crowley, but Nintendo (perhaps unknowingly) allowed the name to remain in the game. Other changes that may relate to censorship issues, are pentagrams turned into stars (or, in one case, a ruby) and a cross into a chalice (while another cross that only served as decoration was removed altogether).
• Beyond the game texts being simplified for the NES port, some of the death texts were edited or altered due to their rather graphic descriptions.

German magazine Data Welt praised the Amiga version's user-friendliness, good graphics and particularly the atmospheric sound, calling the game (translated:) "excellent" and "even better than Deja Vu".Computer Gaming World found the game to be enjoyable and innovative, praising the game's use of graphics and almost exclusive use of the mouse as a way of eliminating frustration. As such, the game was described as "much easier to work with than pure text or text and graphic adventure games."Dragon complimented the game, calling it "a truly horrifying adventure game and mystery that’ll leave you shivering in the dark".

• The Legacy: Realm of Terror