From the premise to the acting, “The Departed” grabs viewers and never lets go, holding their attention in the ultimate cat-and-mouse game until the grisly finale.Borrowing from the Japanese film “Infernal Affairs,” “The Departed” is about two rival informants, one raised by the mob to infiltrate the Special Investigations Unit of the Massachusetts State Police Department, the other persuaded to enter the mob world.

Leonardo DiCaprio (“Titanic” and “Gangs of New York”) plays William Costigan Jr., a police officer, who reluctantly accepts the task of turning rat against an Irish mob run by Frank Costello, played by Jack Nicholson (“A Few Good Men” and “The Shining”).

Costigan’s foil in the movie is Colin Sullivan, played by Matt Damon (“Bourne Identity” and “Good Will Hunting”). Sullivan was guided through school and officer training by Costello and, after rising quickly in the unit’s ranks, aids Costello from within the very organization trying to destroy the mob.

Although both Costigan and Sullivan are playing a dangerous game, it turns even deadlier when both groups suspect rats in their organization and both men must race to uncover the truth.

Backing up the already stellar cast is Mark Wahlberg (“Boogie Nights” and “Invincible”), Martin Sheen (“Apocalypse Now” and “Catch Me If You Can”) and Alec Baldwin (“The Hunt for Red October” and “Beetle Juice”).

Every actor truly captures the heart of a Bostonian and makes viewers believe the actors are Irish, which gives their actions merit and makes the film feel real.

“The Departed” is directed by Martin Scorsese (“Goodfellas” and “Casino”) and takes a departure from his favorite locale, New York, yet perfectly captures Boston’s culture with shots of major Boston landmarks, including Southie, Boston Harbor and Chinatown.

Although the plot alone is reason enough for the film to be well received and entertaining, it is the acting that truly shines as the actors transform into the roles. Even Nicholson, a personality actor whose roles, including this one, are usually the stereotypical Mr. Cool, comes off as his own character, not one seen in his earlier work.

In the past four years, DiCaprio has taken Robert De Niro’s place as Scorsese’s new go-to guy. The partnership between the two looks to be as fruitful as Scorsese’s earlier one with De Niro.

Since 1959, Scorsese, who is considered one of the best filmmakers of all time, has yet to win an Academy Award for Best Director or Best Motion Picture. Yet, with this fast-paced thriller starring an impeccable cast, he should be holding the gold statue come February.