In any event, the result is an amusing YA time-travel cum magic tale. It starts slow, introducing characters gradually but sustains interest, gradually approaching genuine excitement. Yes, reader, it's worth the ride.
The main point of view is that of Melisande Stokes, a young Harvard bluestocking linguist. Her drab existence is upended one day when she collides with Tristan Lyons, a handsome young, straight-arrow military type who has just been ejected from the office of her unpleasant boss, Dr Roger Blevins.
Tristan, on what seems almost a whim, decides to recruit Melisande instead. The black-ops military organisation Lyons is heading is called D.O.D.O. A running gag is that the meaning of the acronym is itself classified. But .. it's to do with magic: magic that used to work but has terminally ceased to function since the introduction of photography c. 1851 .. (blah blah collapses wavefunction blah blah).
It turns out that magic can be restored.
Stephenson here throws in a QM-multiverse substrate for magic - which pretty much falls at the first hurdle since it can't explain how witches could effect time-travel, which they can. Anyhow, magic today can only be restored within a 'Schrödinger cat box' which 'suppresses decoherence', The main characters don't seem to understand how that would work, something probably shared with the reader.
But the authors really don't care about that. They are much more interested in the culture clash between the young activists (Melisande, Tristan, the computer geek guy and a few others) and the military bureaucracy brought in to run the show as it becomes more successful. The novel has an unerring feel for management speak (witches are reclassified as MUONs - Multiple-Universe Operations Navigators) and the impact of political correctness, particularly on historical figures brought to the present ('Anachrons'). Much opportunity for knowing humour.
The plot, such as it is, involves attempts to secure rare artefacts from the past to raise money for the cash-strapped D.O.D.O, a strangely well-informed bank which straddles the centuries, and a plot to restore magic by changing the past. Let us just say that the principal-agent problem looms rather large.
The bad guys (senior military and academics) are convincingly-hissable villains and the heroes winsome and decent. There is also a hint of chemistry in the air, dear reader.
Buy it. You won't be disappointed.
The Guardian's review.