You can slip past the guards to get to the roof, and past the guard dogs inside, if you have the "Chameleon Suit" that makes you invisible. You get it from the doctor at Spyglass Eyewear.
(see the related question)
they are used for keeping the agent held prisonerThe dogs on spy island are in the dock Hideout
at a place in spy island that i do not know of.
But It!
there isn't a fourth agent.
click on him
Click on him
help the kiddnapped agent
go outside and play
you do not you keep the glass
Kidnapper
Once you open the locked vault and rescue the agent, go back to the right and there will be an agent there.
you find it at toupee terrace. :-)