Snowball

The games use a text parser for entering commands at the "What now?" prompt. The parser can interpret more than a thousand words to control movement or actions. It looks at the command, picking out two or three words it knows, ignoring the order, and tries to guess what is meant.

For movement, the usual commands for moving 'NORTH', 'SOUTH', 'EAST' and 'WEST' are available (and their abbreviated forms of 'N', 'S', 'E' and 'W') as well as 'UP' and 'DOWN' ('U' and 'D' respectively) and a number of other directions and 'modes' of movement (like 'JUMP'). For actions, it understands how to pick up objects, opening doors, lighting lamps, as well as dropping objects and wielding them. Additionally, there are commands to invoke 'SAVE' and 'RESTORE' of game positions to cassette tape or floppy disk (for some systems also to RAM), ask for 'HELP', turn off pictures and turn them on again with 'WORDS' and 'PICTURES' respectively, an 'OOPS' command to undo previous commands.

The trilogy is set in the future, when the human race is colonizing the stars. A transport network has been developed for the entire Solar System using accelerator chains, and the "Big 5" nations of Earth have initiated a plan to colonise the galaxy. This is known as the Terran Expansionary Phase. It lasted ninety years from 2120 to 2210.

The first major activity was to launch probes into outer space. The probes reported any Earth-sized planet they encountered during their centuries-long voyage. Each probe was followed by a survey ship ten years later. The ship's mission was to map the planet and, if it was habitable, it would signal Earth and then, while waiting for the colonists to arrive, terraform the planet.

The games were released individually and generally received good initial reviews. Snowball won the Best Text-only Adventure prize at Crash 1984 Readers Awards, Return to Eden received a 90% score in Sinclair Programs, and The Worm in Paradise was rated a Your Sinclair Megagame and a Sinclair User Classic.

When the trilogy was released it received unanimously good reviews from the ZX Spectrum press. Sinclair User gave it a Sinclair User Classic, terming it an "unqualified success for Level 9 and Rainbird." Your Sinclair awarded a Your Sinclair Mega Game, and ZX Computing a Monster Hit. 64 Sizzler.