Grandfather Trent, an elderly man in 19th-century London, runs The Old Curiosity Shop with his granddaughter, Nell, his sole known relative after his son's death. Plagued by existing debts, Trent secures a further loan from the wealthy moneylender Daniel Quilp. Fearing Quilp's harsh retribution for defaulters and unable to repay, Trent flees London with Nell. His primary motivation is protecting his granddaughter from peril and preserving their bond despite poverty.

During their escape, Trent and Nell endure extreme hardship, sustained by the kindness of strangers. Their journey leads them across regions, including Ireland, partly spurred by Nell's hope to find her estranged mother after cryptic news places her in "Paradise." This search uncovers a hidden family past: Trent's daughter-in-law, Rosa, is Nell's mother. Following Nell's father's death soon after her birth, Trent gained custody of Nell while Rosa kept their son, Mario. Both Rosa and Mario were thought dead by Trent and Nell.

Trent perseveres through adversity, including Nell's grave illness. Their flight concludes in Ireland with the unexpected reunion of the fractured family. Ultimately, Trent, Nell, Rosa, and Mario build a life together outside England, aided by allies met during their travels. This resolution achieves Trent's original aim of safeguarding Nell and maintaining their companionship, now encompassing the restored family unit.