Historians have long pointed to Lewis and Clark as the rare example of a dual command that actually worked.

Most such ventures with two leaders fail, the theory goes, because followers need one leader, or two commanders will inevitably have a falling-out.

Michael Pritchett's first novel, The Melancholy Fate of Capt. Lewis: A Novel of Lewis and Clark (Unbridled Books, 416 pages, $24.95), requires readers to follow a similarly delicate navigation with two pieces of fiction in the same book.

One piece is the historical fiction that traces Meriwether Lewis' descent into madness during the cross-country journey and afterward. (In the long-debated question of whether Lewis offed himself or was murdered, Pritchett lands on the side of suicide.)

The other piece is high-school history teacher Bill Lewis' own battle with mental illness; his troubled marriage and troubled teenage son; and temptations to cheat on his wife as he struggles to write a book about Meriwether Lewis.

The result of trying to follow these two strands through randomly alternating chapters: a noble effort that collapses under its own weight.

If the Lewis and Clark expedition had overpacked as much as this novel, the trekkers' bark canoes would have swamped in the Missouri.

The Meriwether Lewis chapters carry a spin of some minor interest to Oregonians who haven't forgotten their elementary-school field trips to Fort Clatsop.

But there's a basic flaw in the modern-day chapters dealing with Bill Lewis: They must carry freight for the Meriwether Lewis chapters. And too often, that load is painful to witness.

There are multiple instances of inexplicable dialogue in which characters must ask Bill Lewis, "So, how's the book going?"

And there are strained parallels between the pains of the explorer's life and those of Bill Lewis. One example of the strain: Meriwether Lewis has an unrequited hard-on for Sacajawea, a.k.a Janey; Bill Lewis, the same for a former student named Joaney.

Near the end, Pritchett writes that Bill Lewis' life "had started splintering into subplots" and that the same thing had happened in Africa, and with Crazy Horse, and with interned Japanese Americans, as well as at My Lai.

The author's conclusion: "Somebody'd lost the thread." Our conclusion: We agree.