The premise of Stephen L. Carter’s new book, The Impeachment of Abraham Lincoln is so audacious – so fascinating – that it virtually begs to be read.

In this reimaging of the Lincoln assassination, the bullet’s trajectory changes by just a fraction of an inch and Lincoln survives. After the country collectively exhales, the “fun” begins. The radical part of his own party presses for impeachment because he has chosen to not punish the south sufficiently in an effort to reunite the country. He is charged with actions that actually occurred under his presidency as a screen – suspension of the writ of habeas corpus, circumventing Congress while borrowing from the U.S. Treasury, placing portions of Maryland under martial law and trying to establish a military-run Department of the Atlantic.

Heady and rich stuff! Mr. Carter is a professor of law at Yale University and his erudition is on full display. The political maneuverings, the impeachment and trial by House Managers, the nuances of removing a sitting president – all are done beautifully by this skilled author. And the key question – can noble ends ever justify ignoble means when the U.S. is under internal threat – is one that resonates today.

However, the core of Impeachment is a mystery. Mr. Carter’s protagonist, Abigail Canner, is a brilliant and beautiful black woman and one of only a dozen black law clerks in the country at that time. Like Miss Marple or Nancy Drew, she is preternaturally able to detect conspiracies, patterns, and intrigues that reach the highest levels of government, even when far more seasoned lawyers can’t.

The result is a rather convoluted subplot (or in many cases, primary plot) in which Abigail – along with another law clerk, Jonathan, the white scion of a northern family – single-handedly crack ciphers, deal with Abigail’s gangster brother, gain Lincoln’s ear (and even meet with him alone), capture the intrigue of high society, and unveil motives of shady politicians.

Real people – such as Dan Sickles, one of Lincoln’s lawyers and a real-life scoundrel – and Salmon P. Chase, the Supreme Court Chief Justice and Edwin Stanton, Lincoln’s trusted secretary of war, are all part of this novel. Lincoln himself, a man given to spun homilies and a far more adept politician than is generally acknowledged – is also portrayed very credibly. When the book delves into legal thriller and political drama, it soars to 5-stars. But the convoluted mystery and too one-dimensional Abigail and Jonathan tether it to earth.