Character guide

Frank Hardy

major

Also known as Frank, Miss Todd Frank Hardy

Frank takes the lead when the boys climb after the raving Captain Royal, and it is his voice that tries reason while rocks tumble down the path. He is the planner of the pair, the one who keeps his head when Joe's impulses surge — until a dead flashlight and a hidden crevice turn him from rescuer into the one who must be rescued. His disappearance in the cavern's depths drives the middle of the book, forcing his brother and friends to search a darkness that seems to have swallowed him whole.

Joe Hardy

major

Also known as Joe, Hardy

Joe is the Hardy who hears footsteps in the night and wakes the camp, the one who scrambles up a cliff path after a madman lobbing boulders. Where Frank calculates, Joe charges — and when Frank vanishes into a pit, it is Joe who steadies his voice and insists they keep searching long after hope thins. His loyalty to his brother is the engine of the rescue, and his recklessness keeps the pursuit dangerous.

Chet Morton

supporting

Also known as Chet, the bashful Chet

Chet is the comic anchor of the group — snoring through the night, grumbling when Joe rouses everyone to hunt a prowler, and taking the theft of the food supplies almost personally. Yet when Frank is missing, Chet's protests fade and he trudges through the caves with the rest, sobered by the thought of what may have happened. His appetite and reluctance make the boys' ordeal feel human rather than heroic.

Biff Hooper

supporting

Also known as Biff

Biff is the practical one in the group, the boy who suggests a roaring fire when three weak flashlights prove useless against the cavern's depths. He is also the one who stacked the supplies and discovers them stolen, his astonishment giving voice to the mystery closing in around the camp. Steady and dependable, he keeps the search moving when grief and fear threaten to stall it.

Fenton Hardy

supporting

Also known as Mr. Hardy, Dad

Fenton Hardy is the quiet authority at the center of the household, receiving Miss Todd's rambling story with patience and shaping her jumbled fears into a theory: that a missing professor may have lost his memory entirely. He counsels caution even as he pursues the hospital lead, restraining Miss Todd's hopes while quietly building the case. His professional instincts frame the mystery the boys stumble into, and his presence lends the adventure its gravity.

Miss Evangeline Todd

supporting

Also known as Miss Todd, Evangeline Todd, Todd

Miss Todd is a flutter of nerves and repetition — muttering "poor Todham" to herself, certain a railway wreck unhinged her brilliant brother, and refusing to wait even for dry clothes before telling her story. Her agitation is both comic and poignant, and when the Hardys produce a possible match in a hospital bed, she rushes off with her hat askew. Her desperate hope that a raving stranger is her brother gives the mystery its emotional stakes.

Todham Todd

supporting

Also known as Professor Todham Todd, Todham, Professor Todd

Todham Todd exists in the story first as an absence — a missing lecturer whose fate pulls his frantic sister Evangeline into Fenton Hardy's orbit. The theory that he lost his memory and hoarded newspaper clippings to reconstruct his own identity turns a routine disappearance into something stranger. His uncertain identity hangs over the early investigation, forcing the Hardys to weigh evidence against hope before they can even confirm whether the man in the hospital is him.

Captain Royal

major

Also known as Captain Royal Todham Todd, the captain

Captain Royal rules his cave like a besieged king, convinced the Hardy boys have come to rob him of money, jewels, and above all his precious papers. His violent outburst when he catches them near the clippings reveals a man whose grip on reality is fraying, yet whose hoard clearly means something he cannot articulate. He matters because he is the mystery's human knot: is he a lunatic, a thief, or the missing Professor Todd himself, stripped of memory and identity?

Carl Schaum

supporting

Also known as Carl, Schaum, The Prisoner Carl Schaum

Carl Schaum is the petty criminal the Hardys already have a score to settle with, and finding him unconscious on the sand near the caves feels like luck dropping into their laps. The tins of meat beside him confirm he has been raiding their camp, tying the thefts to a man the police already want. His capture gives the boys a tangible win and a prisoner to interrogate, even as the larger cave mystery keeps deepening around them.

Tony Prito

minor

Also known as Tony

A friend of the Hardys who helps with boating and adventures.

Mr. Simms

minor

Also known as Simms

A local man who interacts with the Hardys during their investigation.

Iola Morton

minor

Also known as Iola

Chet's sister and a friend of the Hardy boys.

Mrs. Hardy

minor

The boys' mother, supportive and caring.

Mr. Jacobson

minor

Also known as Jacobson

A character encountered during the Hardys' travels.

Lieutenant Patwick

minor

Also known as A certain Lieutenant Patwick, Patwick

A military officer mentioned in connection with the mystery.

Callie Shaw

minor

Also known as Callie

A friend of the Hardy boys, often accompanying them.