Spy X: Proof Positive by Peter Lerangis

In the third book of the series, Andrew and Evie are very close to finding their mother, following clues left by her. But now, the government wing that she works against are on to her. They are leaving clues, disguised as clues sent from their mom. They find out that their father is working against them too. After a class trip to Alcatraz, they discover a secret system of tunnels leading from Chinatown to the Presidio. Will they find their mom there?
--Alex