There's a known glitch in the game that prevents the last TG quest from starting under certain circumstances.
Bottom line is, if you asked the Grey Fox about Jak's diary, he'll never send Amusei to give you the next mission.. There are more details in this thread (with spoilers):
http://www.gamebanshee.com/forums/sh...ad.php?t=75241
If you're on the 360 you're probably hosed unless you have a save game prior to the event that triggered the glitch. A workaround for the PC can be found in this thread:
http://www.gamebanshee.com/forums/sh...ad.php?t=75528