Complex sentence: The Liars soon find out about Alex Drake and that Wren visited Mona and intended on killing her but she promised him that she could get Mary out of prison and feeds them the location of the lair which is underneath Toby's house that he built.
Split into simpler sentences: The Liars soon find out about Alex Drake and that Wren visited Mona and was intent on killing her but she promised him that she could get Mary out of prison. They learn the location of the lair which is underneath Toby's house that he built.