Peterkin, a mischievous elf with mixed body parts, decides to see what would happen if he switched the eggs in the tree-maternity nests. What happens is that there are many surprised mothers, and just as many indignant fathers, when the eggs hatch and each family gets a hatching that resembles neither parent. All fly the, figuratively-speaking, coop and Peterkin is left to tend to all the young birds.