The Sunken Isthmus; or, Frank Reade, Jr., in the Yucatan Channel.

An adventurous scientific expedition sets out after an archaeologist asserts that a former land bridge between Cuba and Yucatan now lies submerged. He recruits an ingenious young inventor who provides a long-endurance electric submarine, and together with a party of scientists they descend into the channel to investigate. The narrative follows their careful underwater exploration of ruins and a sunken city, encounters with treachery and violent assailants, hazardous cave and structural collapses, daring escapes, and the discovery of a treasure cave. The story concludes with the villain outwitted and material evidence recovered to support the original hypothesis.