We did this for ds this year (he was 7, so similar age).
We designed a spy ID card on the PC and had them all set up, then as they arrived we took their pictures wearing those fake glasses/nose things - DH scanned them into the ID card and we fingerprinted them too onto the card. They were a big hit and they were all carrying them at school on the Monday!
We did grandfather's footsteps - that was a good one.
Treasure hunt - this was fab, we did lots of clues and split them into teams (MI5, CIA and KGB but that was more for our own amusement) and they had to solve codes etc around the house and find their way to their own treasure. If anything, we made this too short as it was the hit of the party.
The blindfold game where they have to guess who is standing in front of them by touch was a 'spy instincts' game.
Pass the parcel had spy missions in the layers, that spun that one out a bit.
Code breaking one - my sister set that one up and I can't remember what she did but it was a hit. They were in teams and they had to work out the code first (not all the letters were in the key that she gave them) and then solve the code to find a prize.
If you have space, do a 'laser beam' maze with red wool - they have to get through the gaps without touching the beam. We put the tea table the other side of the maze and they went through one at a time.
Oh, we made the ID cards 3 different colours and that's how we split them into their teams - no arguing about who went in which group.