Midnight Mysteries: Haunted Houdini is one part hidden object and one part adventure game, since it combines puzzles and such into the gameplay. You begin your quest when the apparition of Bess Houdini, Harry's wife, appears to you requesting your help in contacting her long-dead husband. Bess and Harry had a code and agreed to meet up after death, but Harry never made contact. Your quest will bring you face-to-ghostly-face with characters such as the aforementioned Bess, Harry himself, his friend, Sir Arthur Conan Doyle and some of Doyle's relatives, J. Gordon Whitehead, who was Houdini's supposed killer, plus a famous medium of the time and several other contemporaries of the famed mentalist.
Levels will often present you with a list of items to locate in the level, however some will be vague descriptions of items and they will be colored green, whereas the others are in black. Anything colored in blue is hidden from sight. Certain items will be inventory items that you will use for a puzzle later on to progress the story. Ravens are scattered around each area and, when you pick them up, they will provide hints for you, either locating a certain item and highlighting it or showing you what the item looks like, your choice. There are also shamrocks scattered everywhere and if you locate 40 of the 70 in the game, you can unlock Unlimited Mode, which is composed of select key levels and you can return and search for items there. They aren't really unlimited, since you will go through 3 or 4 lists of items, but it's added gameplay regardless.
Puzzles are probably a breeze for gamers well-versed in adventure games, but I am more of a hidden object player, myself, so some of them were a bit tricky for me. They included things like slide puzzles, switch flipping puzzles, standard puzzle piece puzzles and more.