@XelaM - We don't know if Tony is dead, he definitely isn't in the books. I'm thinking surely not.
Re the dirt that Declan has on Rupert, Declan throws a piece of paper in the fire with the word "Perdita" on it. Perdita is the name of an important character in Polo - her mother is Daisy McLeod, who is married to a horrible man called Hamish McLeod. Daisy has 2 younger biological children with Hamish but always told Perdita her father was dead.
SPOILERS AHEAD FOR ANYONE WHO HASN'T READ POLO and wants to!!
Perdita is blonde, arrogant and a fantastic horsewoman. It turns out that some "disgusting old goat" of an art teacher used to hold orgies in the 60s and that Daisy had attended one of them and Rupert and Billy were there. Rupert shagged Daisy and Perdita was the result, but because Daisy had shagged several men that night she'd never told him and she couldn't be sure.
In Polo, The Scorpion finds out and outs Perdita as Rupert's daughter after one of their journos (probably Beattie Johnson) approaches the old teacher (Jackie someone) and finds he's kept his diaries of the time so he tells them that Rupert was there and so was Daisy and bingo, they work it out, especially because Perdita has Rupert's blue eyes, blonde hair and outstanding horsemanship.
Perdita is a complete brat when it comes out (perhaps understandably), calls her mother a horrible old slag and doesn't speak to her for ages. Rupert eventually acknowledges Perdita. But at the time of Rivals Perdita would have existed but be a child I'd have thought. The novels aren't strictly chronological. And Perdita means "lost one" - presumably named because Daisy wasn't entirely sure of her father.
Daisy is a beautiful but scruffy painter who has an ill advised affaire with Drew Benedict, a married Polo player (urgh!) but eventually realises she's in love with Ricky France-Lynch and marries him, becoming Daisy France-Lynch.