You want to organize a surprise party for Harry.
Talk to Sally and ask her a favor. Ask her to go on a date with Harry. She’s not very keen but with some persistence she’ll eventually agree (5/5). Walk to the left and find Harry. Talk to him and ask what happened. Apparently he killed Sally’s parents. Ask him to go out with Sally and reluctantly he’ll agree (5/10).
The couple will take off and you can return home to arrange the party. On one of the barrels is a NOTE. Pick it up (2/12) and read that Steve is waiting in the back yard. Walk to the left and to the back. Use the door down there to reach the main hall and walk north to go to the back yard. Talk to Steve and ask him what he got for a present. He has the same as you so you need to get something else. Ask him about suggestions and he’ll send you to Lucas.
Walk to the left to go to Lucas and ask about his ‘shit’. He’ll offer you everything but tell him to forget it. The ask him for a suggestion and he’ll send you to Harry’s own house. Walk to the right to find his place. Walk to the right to enter Harry’s room and find an INVISIBILITY SPHERE (10/22). Now quickly return home.
Your house is invaded by demons. Talk to the one on the far right and ask them to leave but they won’t. Walk north to find your stereo and switch it off (5/27). They still won’t go. Walk to the left and use the door in the back to go to the main hall. Go north and talk to Steve. Then you’ll hear a noise and think Harry is coming. Use the invisibility sphere on the dark space on the left to hide the sphere (3/30) and as soon as you’re done you’ll have to hide.
When it’s time to jump out of the hiding space, you’ll be greeted by a green monster. And the party turns into a surprise.
Game source: A copy of the game was found here on the internet.