Okay I found the key but I couldn't get the objects to interact (I dont want to give spoilers lol) with the two items I wanted to put together, so that I could actually get to it? I love all the humour you injected in this, nacho average murder lol!
They automatically get used when you click on the key when you have both in your inventory. I wanted to implement a legit inventory system, but I ran out of time so it's strictly click on the key when you have the correct items.
Fun fact: Nacho Average Murder is an actual book a friend of mine found at a Goodwill.