Then he heard Marco and Namur discussing how to deal with the Spade Pirates, and only then did he learn that Ace had actually gone off alone to challenge Whitebeard.
Just at that moment, Marco was telling Namur to take Deuce back first to put some pressure on Ace, while he stayed behind to treat the other members of the Spade Pirates.
Shiki had originally intended to quietly follow them back to Whitebeard's main base, but he happened to overhear Marco muttering to himself: "Ace, is it? Well, I don't know why Pop wants to take you as a son and even hand the position of Second Division Commander over to you. Oh well, Pop definitely has his reasons, so I suppose I can only make you suffer a little less for now."
Chapter 136