There is indeed. It requires just a couple of extra lines into your objective triggers to make it all work.
If for example your objective A trigger is activated when your prisoner is rescued, and you have a trigger that detects this and has the activation field as
"1" ObjStatus "DONE"
Then add into this trigger a simple extra boolean variable;
"1" ObjStatus "DONE"; OBJ1 = TRUE
So when your first objective is complete, it also sets a varible to true. You can use this variable to check if a number of objectives are complete and end the mission. In each objective complete trigger put a seperate variable and set it to true (I use OBJnumber for simplicity). Then you can make an end trigger with the condition;
OBJ1 and OBJ2 and OBJ3
and this will activate your trigger and end the game (assuming its an end trigger.) Note you can also use the && shortcut instead of using the word "and".