The object of Repton is to collect all the diamonds on each screen avoiding the falling rocks and lurking reptiles. You have a limited amount of time in which to complete each screen: the 'Time' indicator starts at 6000 and decreases down to 0; you then lose a life.
There are twelve screens (denoted A-L). Basically, each screen requires you to solve a set of puzzles by determining your routes to collect the diamonds. A rock or an egg will fall if unsupported, and if a falling rock lands on you it will kill you.
On screens A to H, a map is available for viewing. Only one sixteenth of the full area covered by the map is shown on the main screen at any time. On screens I to L, there is no map available.
To view the map, you must first pass over the 'Map' character during the game play; the map may then be seen whenever you press "M".
Screen A is relatively easy to complete. After the screen has been completed, a password is given. Entering this password at the start of the game will then take you straight onto screen B. Likewise, passwords are given at the completion of all further screens.
From screen B onwards, eggs, safes and keys are present. When an egg falls, it cracks upon landing and a reptile emerges. Contact with the reptile is fatal. In order to open the safes, the key must be located. When you pass over the key, all the safes open to reveal a diamond.
It is possible to complete each screen without losing a life.