When I was a kid, many moons ago, I played with Mr. Mystery invisible ink puzzle books. Recently, after looking for them online last year and not succeeding in finding any, I came across them in my local Big W (like Wallmart) and squealed like a kid, not only because they had all four, but because they were $5 each!!!!!
Mr. Mystery and The Return of Mr. Mystery
More Mr.Mystery and Mr. Mystery Line-Up
I’ve only opened the red/orange one as I’m too scared to open all of them, use them, and then have nothing left, so I’m keeping the other three at this stage as collectors items.