G. Callen is one bad ass agent. So bad ass he doesn't even have a real name! Just a letter. G. But the mysterious Callen's embrace of the undercover world can be complicated.

Last night's episode of NCIS: Los Angeles gave us more interesting Callen back story, or Jason Tedrow back story as it were, as a murder prompted G to unretire an old alias.

Coming out of retirement meant unearthing plenty of suppressed emotion. Follow this link for our episode recap if you missed it, then check out our review of "Past Lives" ...

A cab driver dies, execution style, just hours after he sent an email to Jason Tedrow. That would be a man Callen pretended to be four years ago as he worked a case.

Callen spent six months in deep cover as a corrupt military officer, befriending and collecting evidence against three Marines who elaborately stole $5 million in defense funds.

NCIS busted them. Two cooperated to sell out the third, who did not. Marines Gale and Donnelly just got out on parole, while Perez is still in jail. The money? Never found.

Kensi tries to coax info from an important, mysteriously poisoned prisoner.

Gale, the murdered cabbie, emailed Jason Tedrow for help because he'd found the money, supposedly. Kensi suspects Perez might have ordered the hit from prison. Not so.

Callen, as Tedrow, sets out to find the third conspirator, Donnelly. Sam tails his buddy who's gone "lone wolf" and learns that G was in a relationship with Donnelly's sister.

She also has a four-year-old son now.

Through Kristen Donnelly, Callen finds her brother, but he's killed in a drive-by as he talks with G. As Kensi tries to get more info out of Perez, he's poisoned to death in jail.

It seemed like the team put the pieces together a little too quickly - Perez's JAG lawyer stole the money and was eliminating all the "evidence" - but that's how this show is.

The key piece of evidence viewers might have missed was that the same lawyer also repped the man now living with Kristen Donnelly. Always one step ahead of the game.

Callen bids farewell to Kristen Donnelly. And Jason Tedrow.

The most compelling part of the episode was seeing Callen so vulnerable. Taking on different personas leaves him with a certain degree of emptiness inside, as he lacks his own.

As Hetty said, Callen liked being Jason Tedrow best of all. You could see how badly he wanted to tell Kristen the truth, but ultimately did not. Instead, Jason vanished for good.

LL Cool J was also terrific once again as Callen's concerned friend, sidekick and enforcer all rolled into one. These guys bring a new "cool" to the traditional buddy-cop dynamic.

RANDOM THOUGHTS:

• While hipper, faster-paced and in most ways markedly different from the original, the past few weeks have been very character-centered, much like last night's NCIS.
• Daniela Ruah (Kensi) has a birthmark on one of her eyes, according to her IMDB page, making one of them appear darker and the other hazel in certain scenes.
• Eric's enthusiasm for his job, even when relaying awful information, never ceases to amuse. Nor does the fear Hetty can instill in anyone at a moment's notice.

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.