Mae Swansby’s New Encyclopaedic Dictionary yn llawn o gofnodion ffug. Cyn i’r llyfr cael ei digideiddio ar gyfer y gynulleidfa fodern, mae’n rhaid i’r intern ifanc Mallory ei ddarganfod. Yn ei waith, mae Mallory yn darganfod arwyddocâd newydd yng ngeiriau’r geiriadur.

Swansby’s New Encyclopaedic Dictionary is riddled with fictitious entries known as mountweazels penned by Peter Winceworth, a man wishing to make his lasting mark back in 1899. It’s up to young intern Mallory to uncover these mountweazels before the dictionary can be digitised for modern readers.

Lost in Winceworth’s imagination – a world full of meaningless words – will Mallory finally discover the secret to living a meaningful life?