This is a novella about the 2 children of the Phipps and the 2 daughters of the Flintock-Smythes, who are being watched by Katie, who puts 14 yr old Al in charge. Lottie and Al are the same age, Bella, 3 yr. younger than they, and Lily, 8. Recently, Al and his father had patched up a rowboat, and Al has the idea they can play pirates on it. Lottie suggests that, rather than eat before they go, they should have a picnic. They find ham, cheese, bread, and chutney for sandwiches, and a whole apple cake for desert, as well, and fizzy lemonade that Agnes, Al and Lily's grandmother, also made. They pack their picnic and Lottie and Al take turns rowing upstream and steering with the tiller. There are really no beaches on the shore to speak of, but they find a spot for their picnic under a willow tree. Before they can get to the cake, they all fall asleep until wasps waken them, drawn by the apple cake. They get out of there, and head downstream towards home. But all of them are still tired, and fall asleep, and by the time they waken, they're in unfamiliar territory on the river. They try to find a place to tie up, but the current is much stronger and it is impossible to turn the boat and get to shore. Before they know what's happened, they're in the chute leading to the weir, which creates an artificial warerfall. Before they know what's hit them, the boat is airborne. It hits the water hard and all 4 are overboard. Lottie is a very strong girl, sports-loving, and manages to surface but at first, sees nobody. Then she sees Lily's head bob up and go back down. She manages to bring Lily up for air, expel the river water from her gut and lungs, and get her to the duck island in the middle of the lake near Cheadle Manor. Soon after, Al.and Bella come ashore and they make plans to attract attention from the manor, so those hunting for them can mount a rescue. After that, it's a matter of building a fire so the folks at the manor can see them. Lily has gotten too cold, and one of the others moves her around while the others try for dry tinder and kindling amd forewood, and rocks that they might be able to use to light a fire. Once it has started, one of them goes for more dry wood and finds wood ready to build duck huts. They reappropriate it for the fire and are rescued.
Of course, their parents are all upset; the kids didn't ask or have permission to use the boat without adult supervision; none of them thought to leave a note; and they took advantage of Katy's distraction with a new process she needed to work on to continue making a profit (it's implied that the money from the brake seals has dried up and they've had to seek other means of making a living).
Working together, Al rescuing Bella and Lottie rescuing Lily, and to make the fire, they have learned quite a bit that the adults, worried that they might have lost their children, don't see right now.
As the srory ends, we see the bitterness of the old woman, Lady Smythe, the frantic grief of Cass, and the practical attitudes of the Phipps parents, well aware of the scrapes kids get into and seasoned by the grief of the early loss of a child, Katy's expressions of grief because her child died,.an expression that gave her pneumonia, and her grief and confusion for years when she believed Jem was dead, plus her war experience as a WAAC, and the things she saw, the horrors of war, and her fear Al would die, plus her loss of her big brother in WWI, plus Jem's experience in the war and as a POW, and his loss of his arm, make them more relaxed than even Cass, who also lost a brother to the war and drove ambulances as a FANY volunteer, ans is now a widow.
Everything in the valley of the Cheadle River in that area depends on the whims and fancies of the upper class. The people of Lady Smythe's generation are struggling to hold onto the hierarchy that has benefitted them for so long, while the war has been a great equalizer for their children.
The accounts given by the children are aimed at keeping Al from being harmed but will they separate the tenuously rebuilt friendship between Cass and Katy? And will the children ever be able to play with or even visit each other again?