Return the wallet with everything still in it. Half honest is just a slower kind of stealing.

Honesty is not a dial you can set to seventy percent. Handing back a wallet with the cash gone still ends with you keeping money that is not yours, and the good deed becomes the cover for the theft. The owner may never check, but you will know what the gap was for. Partial honesty is usually just honesty arranged for your own benefit.

Hand it over whole and hand it over quickly, before you have a chance to talk yourself into a finder’s fee. There is no version of this where the missing cash feels good later.