Talk to the receptionist and Oppenbot. Go to Doc's room. Doc and Bozo will hide - they think that you are Cletus. You can now take the screwdriver. Use the intercom to call the receptionist. Say you are calling from room no 1 and ask for lunch - the receptionist tells you to choose something from the menu. Ask him to send Cletus' assistant to the top. Leave the room and click on the stairs to reach the room with the pie vending machine. Wait for Oppenbot to go to the reception desk. Talk to the receptionist (in Rufus' outfit) about the menu. Return to the top and use the intercom, pretending to be Cletus. Make an order. Lunch will be served at 12 o'clock. Go down to the restaurant, remove the painting from the wall and use the screwdriver on the nut three times. The receptionist will call Cletus and notify him that dinner is ready.
When Cletus is busy with food, talk to the receptionist (while wearing the disguise). You will get the key to the room. Examine the key in the inventory - unfortunately, this is the key to room no. 9. Show this key to the receptionist. Meanwhile, Cletus will finish eating dinner and Rufus will run away to a restaurant. Cletus will demand the key. Turn the nut twice with the screwdriver - the receptionist will give Cletus the wrong key.
Go back to the reception desk and show the man the key to room no. 5 - tell him that he has just given you this one.. Return to the restaurant and use the screwdriver to set the clock numbers in the correct position (use the screwdriver on the nut twice). Go to the receptionist and you will finally receive the correct key - no 1. Use it to open the door to the Cletus' room (next to the Doc's room).