Lord Walder Frey awakens from a dream to learn of betrayal

Link It To The Plot
Lord Walder Frey awakens from a dream to learn of betrayal
King Maegor I has won the Battle of the Gods Eye. Aegon The Uncrowned is dead and the defeated Lords have either fled or been captured.
Several years after Tywin sees his father being laughter at by his vassals, a young Tywin is at a feast at The Twins with his family.
Jaime visits Tyrion in the cell before the Trial by Combat.
(Situation – Robb Stark and his army of Northmen are near The Twins as they bid to save Lord Eddard Stark.)
(Scenario: Aegon receives a letter from Dorne only to realise that it contains a threat more terrifying than dragons in it. What will he do about it?)