Retrieve Multiple Plugin

Hi ,

i would like to learn  more  about  Retrieve & Retrieve Multiple Message .

From where the plugin fires.?

If i am register a plugin in retrieve multiple and if i try to profile , i could not able to load the page. ?

Scenario ?

in account form contact sub grid will be available. 

i need to sort some some custom logic to display the related contact records using plugin. 

How should i write a retrieve multiple message .?

how to sort the record to plugin?

I would like to have a clear idea about Retrieve Multiple Message . 

please send me some sample code , and how to debug with the process. 

Thanks