Here is the full list of all 21 Hamilton's Great Adventure Demo achievements.
Meet the Agent
Complete the second chapter
Get a gold rating on all chapter two story levels
Earn a treasure score of 8000 on any level
Earn a treasure score of 10000 on any level
Complete one of the optional levels
Defeat Exocet
Defeat a Sentinel
Get a gold rating on all chapter one story levels
Complete the first chapter
Get a gold rating on 5 levels
Complete first puzzle
Complete the third chapter
Complete the fourth chapter
Get a gold rating on all chapter three story levels
Get a gold rating on all chapter four story levels
Get a gold rating on all levels
Collect a total value of 250.000 in treasures
Collect a treasure score of 6000 on the level Tomb of Osiris
Get a gold rating on all optional levels
Defeat an Agent