Tup arrives on Kamino, being brought out in much the same manner that Anakin will be brought out on Coruscant after his duel with Obi-Wan on Mustafar.
Fives confronts Palpatine in the very chambers where Anakin will be reborn as Darth Vader.
Cassandra Truth: Fives is telling the truth about Order 66, but no one will know he was right until it is too late.
Crazy-Prepared: Palpatine goes to insane lengths to ensure Order 66 remains hidden.
First, when Order 66 initiates prematurely within Tup and the clone trooper is sent to Kamino for treatment, he goes with the blunt approach and has Separatist droids storm Tup's shuttle and abduct him.
Then, when Tup is rescued and brought to Kamino, his inside operative Nala Se "takes charge" of Tup and does her best to subtly stonewall any investigation, deliberately using tests that will provide results that indicate a clean bill of health while not providing the results needed to expose Order 66.
Then, when Fives decides to perform an investigation of his own, getting so far as to reveal to the Jedi that something is up, he has Nala Se inject Fives with a drug to make him unstable, before having some one-on-one time with Fives and subjecting him to a Frame-Up to ensure that Fives' credibility is all but destroyed, by way of claiming that they were having a perfectly civilized conversation before Fives suddenly "went mad".
And then, when Fives escapes, Palpatine sends in Commander Fox and the Coruscant Guard to silence him, trusting that Fives' erratic behavior will provoke a knee-jerk reaction - which it does - and get him killed, which it also does.
Downer Ending: Tup and Fives die, Order 66 remains unrevealed, and Palpatine (and by extension Count Dooku) gets off scot-free.