It's like Minesweeper and Clue had a baby named Inspector Parker.
You receive clues in your notebook such as Joe was upstairs from Jane during the murder. So logically you can remove the possibility of Joe being downstairs and Jane from upstairs. In this way, you continue to remove items from the house until you find all the evidence needed to solve the murder.
At higher levels the icons shrink to make room for more items which can sometimes cause you to accidentally remove the wrong item and score a miss (too many and the game is over). However, clicking on a clue in the notebook will enlarge and highlight the corresponding items on the board to make it easier to see.
I have a few issues with timer mode in that the people who QA'ed it should be fired. The clock and timer are underneath the clue descriptions... yeah, you can't see either of them while a clue is selected. Brilliant. Also in timer mode you can make as many wrong guesses as you want with no penalty. This allows you to randomly click on objects until you hit on the right one, defeating the entire purpose of the game.
Despite those big nuisances to my obsessive compulsive soul, I enjoy playing this game. I used to play it as a Java application until the game website removed it so I'm glad to have it for PC which adds more levels and a much larger window.