The phrase "little mystery" refers to something that is not easily understood or explained, but is not too difficult or complex either. Full definition
It is a title that leaves little mystery as to the content of the seminar which I found refreshing in this age of «link bait» headlines and come - on offers. (authorimprints.com)
Amazing story and characters but it was very little mysteries. (metacritic.com)
Maybe it's the creepy little mystery bits of neon - colored candies. (vintagevictuals.com)