U3 - Past Perfect
Theory and the use of Past Perfect:
http://www.helpforenglish.cz/article/2010060101-predminuly-cas
Go throuhg exercises:
http://www.helpforenglish.cz/article/2007091801-minuly-a-predminuly-cas-1
http://www.helpforenglish.cz/article/2007091802-minuly-a-predminuly-cas-2
http://www.ego4u.com/en/cram-up/tests/past-perfect-simple-1
http://www.ego4u.com/en/cram-up/grammar/past-perfect-simple/exercises