Nine killings of homeless men with their faces painted yellow and a tag labeled ``U.S.S.R.'' stuck into their clothing, and Midtown North still doesn't have a clue. But when the tenth Yellow-Man victim turns out to be Dr. Hektor Stefanopolis, the eminent scientist who'd just left the Armitage Broadcast Center after plugging his new book, Running Out of Time, Capt. Dennis Fillingeri finally gets interestedand so do Morning Watch news director Abby Abagnarro and his producer and ex-wife, Ike Tygart. What does Stefanopolis have to do with all those street people? Is the latest killing a copycat crime? If (as Fillingeri now says) all the victims were stabbed after death, what killed them? Who got close enough to Stefanopolispresumably during the Morning Watch tapingto kill him the same way? And how much can Abby afford to tell Fillingeri and the FBI about the homeless mugger who accosted him on the way to work that morning with a few wild hints about the Yellow-Man killingsand then appeared large as life standing behind Fillingeri on the latest crime- scene tape? Mercifully less coy than Abby and Ike's debut (Until Death, 1994)and just as clever, effervescent, and jam-packed with acid- spiked tidbits about broadcast news.