Can't access file contents

Hi,
I'm sorry if this has already been answered. I've gone through every other thread that looks like it could've been helpful, but I'm not that tech-savvy so I may have missed it.
Anyways, I purchased and used Espionage aaaaages ago, used it on the one file I really needed locked, but now I've forgotten the password to the file.
Also, I can't find the file - I only have the spareseimage. It's 18 mb, so I know there's stuff in it... but when i double click it, nothing happens (it's programmed to open with DiskImageMounter, which works with other files), and it's probably going to be locked.
What can I do!? I still have my Espionage password.
Thanks
I'm sorry if this has already been answered. I've gone through every other thread that looks like it could've been helpful, but I'm not that tech-savvy so I may have missed it.
Anyways, I purchased and used Espionage aaaaages ago, used it on the one file I really needed locked, but now I've forgotten the password to the file.

What can I do!? I still have my Espionage password.
Thanks