There are three kidnapped spies to rescue, in order : the one at the Docks, the one atop the electrified building on Toupee Terrace, and the one in the rooftop greenhouse above Balding Avenue.
(see the related questions for each)
go outside and play
Once you open the locked vault and rescue the agent, go back to the right and there will be an agent there.
You can't open the door, but you can go over it.
The second rescued spy (in the electrified building on Toupee Terrace) gives you the grappling bowtie, which you use to rescue the third and final missing spy.
click on the cherry bomb on the roof tops push it in front of the cage it will blow up and BAM you have the third agent
at a place in spy island that i do not know of.
when you rescue the 2cd. spy he gives it to you
But It!
there isn't a fourth agent.
Director D of course
you rescue one of the spys and he will give it to you
Rescue the first spy. He is locked in a vault...but there is a hole in the ceiling!