Today's daily deal brings the game down from £18.99 to £17.09.
Use the voucher: "DECEMB-202014-GREENM" for a further 20% discount, bringing the game down to £13.68. Not a bad price considering it was released relatively recently :)
Note: I believe the game is a Telltale code, and not a Steam code
ANOTHER NOTE: The Daily Deal is now over, but the voucher is still applicable, meaning that you can still get this for £15.20