"The Case of the Missing Flip-Flops"

Somebody is wearing mismatched "Flip-Flops" (I carefully choose to substitute this word in place of the word thongs...which is what they really are. There could be some confusion with the double meaning.) Anyhow, so ummmmmmmmm......Tiff thinks Leana has her shoes and when Leana gives them to her, they're two different sizes. So, Leana comes back to swap the one shoe with the other so they will each have their 0wn black flip-flop. When they get together, they realize that the odd pair was neither of theirs but a set that belonged to somebody else. That somebody else is wearing one of Tiff's shoes and one of Leana's. So...........The search is on! Who has the missing flip flops???????