When a government official disappears in the London tunnels, after several reports of missing people in the same location, Scotland Yard start to take the matter seriously, along with a couple who stumble into a victim by accident.
| Actor | Role |
|---|---|
 Donald PleasenceInspector Calhoun | Inspector Calhoun |
 Norman RossingtonDet.Sgt. Rogers | Det.Sgt. Rogers |
 David LaddAlex Campbell | Alex Campbell |
 Sharon GurneyPatricia Wilson | Patricia Wilson |
| HHugh ArmstrongThe "Man" | The "Man" |
| JJune TurnerThe "Woman" | The "Woman" |
 Clive SwiftInspector Richardson | Inspector Richardson |
 James CossinsJames Manfred O.BE. | James Manfred O.BE. |
| HHeather StoneyP.C.W. Alice Marshall | P.C.W. Alice Marshall |
| HHugh DicksonDr. Bacon | Dr. Bacon |
 Christopher LeeStratton-Villiers, MI5 | Stratton-Villiers, MI5 |
| JJack WoolgarPlatform Inspector | Platform Inspector |
 Ron PemberLift Operator | Lift Operator |
 Colin McCormackPolice Constable 1 | Police Constable 1 |
| GGary WinklerPolice Constable 2 | Police Constable 2 |
 James CullifordPublican | Publican |
| SSuzanne WinklerProstitute | Prostitute |
| GGerry CramptonTunnel Worker | Tunnel Worker |
| TTerry PlummerTunnel Worker | Tunnel Worker |
| GGordon PetrieTunnel Worker | Tunnel Worker |