Sands of Death - S3.E7

Tyrig plans to use a nerve gas to seize power on Mars. Raeburn discovers that Tyrig and his men have set up base on the Martian moon Phobos and Dart is sent to investigate. Dart and his crew are captured by Tyrig, who wants to use the Galasphere to spread the gas. Refusing to co-operate they are placed in a dungeon which slowly fills with sand