Find Eva's hideout
Protect the van containing the Big Boss's body
Let's start the third act. First you will get the young Snake's Face Camo, casual clothes and shortwave radio. However - we won't use it. After a few steps you should spot an agent you have to follow.
Hide behind a car and wait till the agent cross the street. You can stick close to him, but in case of trouble you can hide behind the trash cans.
Passing the first corner watch out for the can [A] - don't knock it. When you get an info from Otacon, pointing that the agent [B] is not going any further, till the soldier [C] is guarding the street - use the MG.
Turn on the camo, drive the MG nearby the soldier and stun him. Wait for the agent to move along and go. There is another soldier near the park [A]. Eliminate him silently - tranquilizer gun should do the trick.
Keep following the agent. He will try to relieve himself buying you time to take down another blockade. Crawl onto the small hill [B].
There two soldier guarding the gate [A] - [B]. Take them out silently.
Then you should find a small square with some soldiers and a helicopter. Avoid being detected and follow the agent staying close to the wall on the right.
There are another soldiers trying to catch the agent. You have to eliminate them, first the [A] one, then [B]. But even when the agent is capture - you can set him free.
A few steps away the agent is going to turn into the gate and enter the backyard [A]. Wait for him - after a few seconds he would return - dressed like a soldier.
All of this time keep following slowly the agent, who should pass some guard post. At some point three patrolling soldiers would join him [A]. But don't panic - just follow him.
One by one - the soldier would start to departure from the agent. Now it's time to check your barrel-hiding abilities - there is going to be some patrols in cars. As soon as you heard the engine - hide yourself inside the barrel.
At last - the agent has arrived at his destination. Wait till he change his clothes and go with him to meet Eva.