If it is the Three Class 777 that you are on which I think it is (Basically the 777 with no First Cabin but just Club, WTP and WT) then row 24 is at the back of the mid cabin with the toilets immediately behind. 24D is infact a crew jumpseat and is occupied by a crew member for take off and landing. For the rest of the flight its just a standard seat with Video screen and controls however the seat back is fixed and uncushioned.
Its a good row to sit in if just the two of you as you get a bit of extra space to put the feet up but it is just infront of the loos so may get a big stinky or crowded!