"Monk." Tonight at 10, USA Network.
'Monk" is back.

Not just for a new season, but in terms of quality, too.

Tonight's fourth-season premiere (USA Network at 10) returns "Monk" to fine form after a slump that dragged at the show like a riptide most of last season.

And it does so while giving guest star Jason Alexander something that otherwise has eluded him: a post-"Seinfeld" TV comedy role that's worthy of his talents.

In tonight's episode, Alexander comes on the scene - the crime scene - almost immediately, pushing aside uniformed cops, CSI investigators and Tony Shalhoub's obsessive-compulsive investigative consultant, Adrian Monk, to offer unsolicited analysis of the crime.

Alexander is playing private detective Marty Eels, a slovenly guy whom Peter Falk's rumpled Columbo would consider improperly dressed.

Marty is as messy and gross as Monk is fussy and neat - and where germophobic Monk looks at a pile of dog droppings at the crime scene and is stricken to the point of immobility, Marty looks at the same pile and sees fresh evidence.

From there, Marty follows one clue after another, each more outlandish and arcane than the next, with Monk sputtering and protesting all the way.

When one of Marty's hunches leads to a missing car, Marty reaches under the wheel well to retrieve and taste some mud - to ascertain, he says, where the car has been.

Monk is grossed out that Marty would do that, and unconvinced of the accuracy of his unconventional methods.

The two of them working, together and yet very separately, is one of the funniest odd-couple detective teamings since Tom Selleck guest-starred as ultra-idealistic Lance White to bedevil James Garner's pragmatic Jim Rockford on "The Rockford Files."

Shalhoub, given the chance to follow rather than lead the investigative team as a very exasperated Monk, has a great time with Alexander's slimy Eels.

Viewers will, too, and should be very happy to have "Monk" back near the top of its game.