Transported into strange underwater worlds by the half a sea shell William owns, Mary and William conduct a seemingly hopeless search for the other half of the shell.
- ISBN10 0330251007
- ISBN13 9780330251006
- Publish Date May 1977 (first published 1 January 1974)
- Publish Status Out of Print
- Out of Print 8 April 1992
- Publish Country GB
- Publisher Pan Macmillan
- Imprint Macmillan
- Edition New edition
- Format Paperback
- Pages 155
- Language English