Hannah Rothschild never quite solves the mystery that comprises the heart of The Jazz Baroness. But her seductive documentary about the profound friendship between her British great-aunt and bebop pianist extraordinaire Thelonius Monk provides so many bits of pleasure along the way that we don't particularly mind.

Made for the BBC and airing half a dozen times on HBO2 over the next few weeks, The Jazz Baroness evokes a particular New York state of mind ‹ Manhattan in the 1950s and '60s ‹ when a hip, civilized night on the town meant a jazz quartet and straight Scotch. Needless to say, a soundtrack filled with lovely, one-of-a-kind Monk performances adds immeasurably to the vibe.

The midcentury setting provided unexpected common ground for the African American son of sharecroppers and an affluent, strong-willed British Jew, Barnoness Panonnica (Nica) Rothschild de Koenigswarter, whose family was touched by the Holocaust.

Nica and Monk's bond allows for the briefest of riffs on black-Jewish alliances, notably those formed during the civil rights movement. The Jazz Baroness is less interested in the broader social ramifications of the duo's relationship, however, than in their enigmatic personal connection.

The story begins in England, where Pannonica Rothschild was born into fabulous wealth in 1913. Banking was the Jewish family's longstanding business, and the Rothschilds had quietly accrued a jaw-dropping fortune, rarefied status and enormous influence.

"We were brought up in great luxury, but no liberty, and great discipline," recalls Dame Miriam Rothschild, Nica's elderly older sister, in an interview taped late in life.

We infer that Nica chafed at the structure and expectations ‹ Rothschild women couldn't work in the bank or go to college ‹ and sought her own identity. Although she participated in the debutante circuit and married well, she was a trained flier when she wed the French envoy Baron Jules de Koenigswarter in 1935.

They lived in France and started a family, but during the war, Nica and the children escaped to New York. She eventually made her way to Africa, where the baron was fighting with the Free French, and they were together in Germany when the war ended.

The defining moment of Nica's postwar life was hearing a piece called "'Round Midnight." Two years later, in 1954, when its composer performed in Paris, she flew from London to meet him. After an electric week with Monk, Nica jettisoned her English life, husband and children and relocated to New York.

Monk was married, and The Jazz Baroness assembles some evidence and testimony that, although Nica was his patron, protector, occasional muse and eternal friend, they weren't lovers.

That bit of gossip is less compelling than the whereabouts, upbringing and emotional turmoil of the five kids Nica left behind. It's regrettable that they wouldn't talk with their filmmaker cousin, suggesting some longstanding resentment.

The filmmaker does come across some cards and correspondence that indicate that Nica did have a relationship with her children, and that one or more of them lived with her in Manhattan for various periods, but that part of the picture never comes clearly into focus.

What we do learn, from jazzmen like Sonny Rollins and Archie Shepp, is that Nica was a fixture on the downtown jazz scene. She was unwavering in her assessment of Monk's talent and importance, but also helped countless other musicians with everything from groceries and the occasional rent check to ‹ in the case of Charlie Parker ‹ taking the rap for the marijuana found in the car they were taking to a gig.

If there were any doubts about Nica's allegiance to her musician friends, or her standing as the black sheep of the Rothschild family, this episode erased them once and for all.

The facts paint a clear picture in this case. But the core of Monk and Nica's extraordinary 28-year relationship eludes Hannah Rothschild's swoops, forays, interviews and memorabilia-digging.

Of course, we can never know what bonds and binds two kindred souls, regardless of whether they are of different races and come from different continents and classes. In The Jazz Baroness, it is enough to have entree to their world.

For the record, some of the most compelling archival footage consists of clips from Straight No Chaser, Charlotte Zwerin's terrific 1988 documentary about Monk.

The Jazz Baroness premieres Nov. 25 at 8 p.m. on HBO2, and repeats Nov. 29 at 8 a.m., Nov. 30 at 3 p.m., Dec. 3 at 6:30 p.m., Dec. 11 at 7:45 p.m. and Dec. 16 at 1:30 p.m.

Michael Fox is a San Francisco-based film critic.