Educated at home because of the supposed aftereffects of a childhood illness, Alec grows up friendless in a home riven by the arid marriage of his domineering mother and gentle but detached father. A chance encounter with Jerry provides his only childhood friend, a friendship bonded by their mutual love of horses. Eventually, Alec's mother discovers the friendship, insists that it is unsuitable for a boy of Alec's class, and terminates it.
As Alec matures, he grows closer to his father; they both resist his mother's pressure on Alec to join the British Army and serve in World War I. Eventually, she reveals a family secret, one that pushes Alec to enlist and become an officer in the same regiment as Jerry. Jerry's reasons for joining up are at once prosaic -- his mother needs the money -- and patriotic: Jerry has joined the IRA and wants to learn how to use a gun.
They rekindle their friendship and become closer, finding ways to ride together in the French countryside. As interludes with Jerry and a fellow officer named Bennett become Alec's refuge from the pointless squalor of trench life, the regimental major applies continual pressure on Alec to end the friendship. Eventually, Alec must choose between Jerry and the obligations of class, rank, and religion.
Through a series of confrontations and secret meetings between the friends, Johnston brilliantly contrasts the hollowness of social roles with the humanity of friendship. The descriptive passages are brief but telling, and often serve to introduce superbly constructed dialog:
"The sky was immense. Huge white clouds, their bellies stained black by the drifting smoke from the land, floated with dignity across it. Away to the left the cathedral at Ypres pointed accusingly at heaven. Far, far beyond the town on the horizon a line of white charming puff-balls appeared and disintegrated, a background to the grey tormented landscape. Nearer and to the right the big guns were blasting away and grey smoke swirled up to the clouds. Some farmhouses were burning gaily. No living thing moved. By some freak of the wind we could hear only the gentlest rumbling of the guns, not even enough to twitch the horses ears.
'Jay,' said Jerry.
'Some great show, eh?'
'In an odd way it's almost beautiful.'
'It's a game I'd rather be watching,' said Jerry.
'I don't know,' said Bennett thoughtfully.
"We all continued to stare at the changing patterns of smoke and cloud. My horse became impatient and pawed angrily at the ground, shaking his head with a fine jangling of harness. I realized that I was bitter cold.
'Well, I'd rather watch it than be in it, and I'd rather be home than either.' Jerry sounded as if he meant it.
'Ah, fer Christ's sake!'
"I think there's something rather splendid about it all. There's always the chance that one might become a hero. Doesn't that stir your blood?'
'I can't say that it does.'
'I'm cold,' I said to them.
'I take it then that it doesn't stir your blood either.'
"He pulled his horse's head round as we spoke and we set off across the hillside.
'Not a movement.'"
Babylon is not a horror-of-war book, but it expertly applies war as a setting that builds relationships at the same time that it destroys them. A marvelous accomplishment from a highly-skilled writer at what must be the top of her game.