Very disappointing, and yet not a dreadful book either (I've read five other McEwan's, all 4* or 5*).
The narrator is preparing the memoirs of his dying mother-in-law and particularly wanting details of a terrifying encounter with black dogs more than 40 years ago that changed the direction of her life, and therefore that of her husband and children.
Jeremy describes his own childhood, contrasting it with that of his wife, and tells of trips to the care home to talk to his mother-in-law, recounting snippets of her life. As the book progressed, I became increasingly annoyed about this big secret and heavy-handed metaphor that would, presumably, be revealed at the end, thinking it would probably be an anticlimax. And it was.
Other than that, the main theme is honesty - to oneself and to others. June and Bernard (Jeremy's parents-in-law) joined the Communist party at the end of the war. For me, the most effective passages were those that looked at how people twist or ignore the truth to maintain their faith in something, and the tensions between scientific rationalism and more instinctive spiritual aspects. McEwan points out that "Laboratory work teaches you better than anything how easy it is to bend a result to fit a theory", acknowledging that "rationalism is blind faith". Jean and Bernard were very different, except "their capacity, their appetite, for belief never diminished", though not necessarily in the same things. I was also stunned and delighted at the idea of "The Socialist Cycling Club of Amersham".
Perhaps related to that, Jeremy is very conscious of one generation repeating the faults of a previous one, though he sometimes uses that as a convenient excuse. For example, almost losing touch with a young relative because "I could not bear to undergo another parting from X. The thought that I was inflicting on her the very loss I had suffered myself intensified my loneliness".
One obvious topic that is never really addressed is depression, which is odd, given the title: the book even mentions that "the black dog" was how Churchill personified his depressive episodes.
There are snippets where McEwan's perceptive writing shines though; it's the book as a whole that doesn't work for me. To end with the good writing:
* "The companionable love-making that is the privilege and compromise of married life."
* A terminally ill person was "buried in a sleep that had itself been smothered in an illness" so on waking, "she had to reconstruct her whole existence, who and where she was."
* The liturgy at a funeral was "a succession of brilliant phrases, book titles, dying cadences that breathed life, pure alertness, along the spine".
* An unhappy family entering a restaurant was "a luminous envelope of familial intensity".