Kate, Rachel, Rose, and Claire are getting used to what remains of their so-called lives. While they may never be “normal” again, at least they can count on each other - no matter what.
You have to use it last. Otherwise, 
it's not a secret weapon.
Die ist mein Ass im Ärmel.
Kommt also ganz zum Schluss dran.
Debes usarla al final.
De otra forma, no es un arma secreta.
Elle est secrète car on la sort à la fin.
Você tem que usar por último,
ou não é uma arma secreta.