William Milhouse and his brat sister Miranda are uprooted from London city life when mother Kate accepts a job with Arnold Talbot, the best friend of their late father Henry, who expected to wed her. The Milhouses stay on the grand Devonshire estate of widowed lady Augusta Pritchett, whose grumpy butler Humphrey claims to hate children. Engineer Geoffrey Hynes strikes an instant friendship with William, which is however cruelly sabotaged as well as a crucial contract by his ex Vivian Palmer out of jealousy when he falls in love with Kate.