Walk north twice and ring the bell. Try to go east and Phong will lead you to the Living Room. Wait here and you will be taken to Linder's office. Sit on the wooden chair. Read the note when he hands it to you. Show the matchbook to Linder, then keep waiting until Linder is shot.
Stand up and press the button. Get the keys from Phong when he enters, then examine the clock. When Phong leaves again, examine the keyhole. Wait until Duffy arrives, then analyse the powder. Examine the window and take the green wire.
Now go west and north twice. Open the Butler's door, then go west and read the mystery book. Drop the telegram, note and mystery book, then take the receipt. Walk east twice to enter Monica's room, then unlock and open the back door. Continue east and south twice, and pick up the gun.
Next walk west twice, north and east. Unlock and open both the garage door and the workshop door, then go east into the workshop. Examine the spool of wire.
Wait here for Monica. Follow her when she leaves, until you reach her bedroom. Wait for her to come back out of her bathroom, then ask her about Mr Linder. Wait again, then follow her when she leaves - as soon as you reach the office, handcuff her. Now search Monica for the key. Unlock the clock and open it - she has already removed the gun, so search her for that too. Wait for Duffy to return, then arrest Monica.