When a frustrated public servant is fired from his meaningless job, he decides to become a masked vigilante, protecting his neighbourhood.

Okay... here's my next reworking:

After witnessing how easily the system let?s down someone he loves, a frustrated social worker leaves his job and becomes a masked vigilante.

Agreed with all the above.

Also what is at stake? What will happen if he doesn't protect the neighbourhood? What will happen if he does?

Hope this helps.

I like this is the most out of your three as well, but it risks being dangerously close to being "Super". Why does np he need to protect his neighbourhood... Hope this helps.