You can't use a hyphen as part of a package name. You have a package named "Plug-in.pm"; but it's looking for "Plug.pm", after which it will substract the result of &in::Find.

Beside that, you may want to see the answers to " How do I keep my own module/library directory?" and "How do I add a directory to my include path (@INC) at runtime?" in perlfaq8.

Good luck :)