Past Perfect Tense :  This tense is used to denote an action completed in the past before a certain point of time in the past.  Past perfect tense has two past actions ( sometimes one may be hidden or implied) of which one is more remote when viewed from the present time and this particular ‘ more remote action’  is explained by past perfect tense.) To put in other words, here there are two past actions of which one happened earlier than the other.  The action which happened earlier is used in the past perfect tense and the other in the simple past tense.

Examples.

• She had finished her homework before her teacher arrived.(i.e  here there are two actions (1) finishing of homework (2) arrival of the teacher. Finishing of homework happened earlier than the arrival of teacher.  Therefore the  earlier action (finishing of homework) is explained in the Past perfect.
• He had offered all-out support for my venture before anybody else.( i.e his support came earlier than others’ support)
• When we arrived for the function Mukesh wasn’t there.  He had gone home.( i.e Mukesh”s going home happened earlier than our arrival , so that is explained in the Past Perefct)
• Tom had just got home when his wife phoned him.  He had been in Kochi.(Note the two actions,(1) Tom’s getting home (2) wife’s phoning. Of the two actions , the action marked No.1 took place before the No 2 action. Viewing from the present, action No.1 is more remote than the No 2 action. Therefore action No.1 is explained in the Past Perfect.