Following the destruction of a WASP submarine, Troy and Phones are sent to investigate. They are soon captured by an enemy submarine in the form of a gigantic fish, which takes them to the underwater city Titanica. There, they meet Titan for the first time.
| Name | Type | Role | |
|---|---|---|---|
| Gerry Anderson | Writer | ||
| Sylvia Anderson | Writer | ||
| Robert Easton | Guest Star | ||
| Don Mason | Guest Star | ||
| Ray Barrett | Guest Star | ||
| Alan Pattillo | Director |