What's on TV this week

There are many things unclear about Vince Chase, the rising young heartthrob on HBO's new comedy "Entourage."

Just how good an actor is he? How smart, hardworking and committed to his craft? How likely to wield staying power as a Hollywood "It" lad?

One thing's for sure: Vince is having a blast with his sudden money and fame, particularly in the company of the pals he shares those blessings with.

Adrian Grenier ("Drive Me Crazy") scores as Vince, the impossibly dreamy star of a new action film called "Head On" whose splashy premiere frames the first "Entourage" episode at 9 p.m. Sunday.

Other shows to look out for:

World War II drags on, even though the lovely English countryside where Detective Chief Superintendent Christopher Foyle is in charge seems far removed from the action. But those pastoral surroundings aren't immune to war-related murder and intrigue, as the splendid "Foyle's War" returns for four new cases on PBS' "Mystery!" at 8 p.m. Sunday (check local listings).

The first episode of "The Days" (which, like those to come, chronicles a single day in the Day family's lives) finds this bunch with their hands full. Jack, the head of the household, impulsively quits his hated high-paying job as a lawyer. His beautiful wife, Abby, is having problems with her own high-pressure job when a certain health issue arises. All three children are blessed with varying degrees of brilliance, which each will call upon to navigate the respective challenges imposed by this particular day. Airing at 9 p.m. Sunday on ABC, the premiere heaps the Days' plate high (here's hoping future days are a little more relaxed).

MC Lyte is on the bill as a new season begins for "Russell Simmons Presents Def Poetry." Also appearing: Daniel Beaty, Rives, Nafessa Monroe, Zena Edwards, Oscar Brown Jr., Amalia Ortiz, Black Ice and Mark Gonzales. Winner of a 2003 Peabody Award, the series airs at 11 p.m. Sunday on HBO.