There’s a bizarre love triangle at the center of “The Proposal,” an odd and fascinating documentary by Jill Magid in which the filmmaker, a conceptual artist whose practice often addresses power structures, is both the storyteller and the story (or at least a huge chunk of it). In one corner of that love triangle is Luis Barragán, one of Mexico’s greatest architects and, since 1988, a dead person: one whose professional archive — or, rather, access to it — is the issue around which the film revolves.

In the other two corners are two women: Magid herself, a passionate fan of Barragán’s work, which is known for its serene beauty and emotional use of color, and Federica Zanco. Since 1995, Zanco has controlled access to Barragán’s archive, restricting access to it as she prepares to publish a catalogue raisonné of his work.

Zanco’s husband, Rolf Fehlbaum, the former head of the Swiss furniture company Vitra and a current board member of the family-owned firm, is said to have purchased Barragán’s papers for Zanco as an engagement present. Whether that’s true is one of the many enduring mysteries touched on by this film. What is undisputed is that, decades later, Zanco is still working on the book, and the archive is still, for the most part, off limits to everyone else. In a curious aside, Magid notes that the foundation Zanco established to oversee the architect’s papers has trademarked Barragán’s name, minus the accent mark.

Magid’s film, which is both a piece of performance art and a documentation of that performance, tracks the artist’s correspondence with Zanco in an effort to persuade her to grant Magid access to the archive, or, more critically, to return it to Mexico, where many in that country feel it rightfully belongs. The story of how it was ever put up for sale in the first place, for a reported $2.5 million, is a good one, and is dispensed with early in the film.

Spoiler alert: Magid’s back-and-forth with Zanco doesn’t work. Zanco repeatedly — and politely — puts Magid off, citing the scholar’s need to focus on her research. Their communications culminate in a face-to-face meeting on the campus of Vitra’s modernist headquarters in Weil am Rhein, Germany, during which Magid makes the strange proposition referenced in the film’s title — one inspired by the romantic story of the archive’s purchase.

With the permission of Barragán’s estate, Magid exhumes a small portion of the late architect’s cremated remains, fashioning them into a synthetic diamond that she presents to Zanco as a kind of counterproposal to Fehlbaum’s (perhaps apocryphal) gift: Accept this diamond, a little piece of Barragán, in exchange for returning the archive to ­Mexico.

Ghoulish? Perhaps, but also conceptually brilliant.

Zanco’s answer, of course, is hardly the point. Both she and Magid seem to agree that the offer is beautiful regardless. “The Proposal” also follows Magid’s preparations for the artist’s 2016 art exhibition of the same name at the Kunst Halle Sankt Gallen art gallery in northeast Switzerland. There is a hyper-meta quality to this documentary that will probably appeal to fans of navel-gazing conceptual art — or just devilishly pointed black humor.

But there’s more to “The Proposal” than a good laugh. By interrogating Zanco’s unusually draconian control, Magid raises issues of national heritage and the ethics — perhaps even the morality — of sealing up intellectual property in a tomblike vault.

Who should have access to an artist’s legacy? That’s only one of many good questions raised in this mesmerizing exercise in artistic interrogation.

Unrated. At Landmark’s West End Cinema. Contains nothing objectionable. 83 minutes.