Seastalker was the 12th game released by interactive fiction pioneers Infocom. It was the only Infocom game marketed primarily towards children, and the only one characterized by the company as being "Junior" level difficulty. Seastalker also marked the first use of the term "interactive fiction" in official advertising.
Co-writers Stu Galley and Jim Lawrence came from very different career paths. Galley was a long-time Infocom game designer/programmer (or as the company called them, "implementors", or "imps"), responsible for the successful and acclaimed murder mystery The Witness. Lawrence was an exceptionally prolific novelist, most notable for having written the "Tom Swift, Jr." series about a teenage inventor. The series wasn't quite as successful as the original "Tom Swift" series from which it was derived, but did well enough to warrant the publication of 33 books.
Infocom, seeing the potential of products that could appeal to a younger market, attempted to license the Tom Swift property, but found the asking price to be too expensive. Thus, they hired Lawrence as co-author and developed Seastalker, which would also be an adventure story about a young inventor. Seastalker would be the second Infocom game, after Infidel, to be classified in the "Tales of Adventure" genre.
Seastalker opens by asking the user to provide his or her name, which is then used throughout; thus, "you" are the hero. The Aquadome, an underwater research station, is being attacked by a sea monster. You and your sidekick Tip must hop into your mini-submarine, the Scimitar, and save the day. This proves to involve the exposure of a traitor among the Aquadome researchers.
Seastalker introduced the innovation of "split-screen" technology (programmed by future "imp" Brian Moriarty) to the Infocom virtual machine. In many scenes, a depiction of the Scimitar's sonar display takes up the top of the screen, while the user can type commands in the lower half of the screen.
Other Infocom games had "InvisiClues" sold separately, where puzzle solutions were written in invisible ink that users could uncover. Seastalker, intended for a younger audience, came with "InfoCards" and an "InfoCard decoder" that worked similarly. Tip, as befitting his name, will also often provide hints.
As had become traditional for Infocom, Seastalker's packaging contained collectibles (or, as they were referred to, "feelies") to help set the mood of the game. Seastalker's "feelies" were:
- The InfoCards and InfoCard decoder, as described above
- A "Discovery Squad badge" (actually a sticker)
- A map of "Frobton Bay", where the action takes place
- The Scimitar's "logbook", including:
- A letter from "the President"
- A diagram of the Aquadome
- Descriptions of the Aquadome employees
- Descriptions of the various gadgets available in the game
- A log where players can keep track of their games and scores