The Hardy Boys: The Mystery of the Flying Courier (1977)

S01E09 - Frank thinks he sees a girl whom he knew years ago who went missing, whose parents hired his father to locate but couldn't. When he tries to talk to her she claims that she is someone else. So he and Joe try to follow her but someone tries to kill them so they think she's mixed up in something. IMDb.

The Hardy Boys: A Haunting We Will Go (1977)

S01E08 - Nancy revives a play in a theater that is supposed to be haunted. Actors from the original cast return to do the play. They seem to have intentions rather than the play, which makes Nancy suspicious and determined to discover the secret of the phantom. IMDb.

The Hardy Boys: The Flickering Torch Mystery (1977)

S01E07 - While investigating the disappearance of a sound technician, the Hardy Boys find a link to a rock band he was working for. IMDb.

The Hardy Boys: The Secret of the Whispering Walls (1977)

S01E06 - Nancy's aunts are going to sell their property. The day before the deal is reality, a burglar steals all documents. Nancy goes to her aunts to explain. One aunt shows very discomfort, and speaks about voices in the walls. IMDb.

The Hardy Boys: The Disappearing Floor (1977)

S01E05 - While investigating the disappearance of a missing scientist, the boys begin to doubt their senses when they discover an isolated estate loaded with bizarre illusions. IMDb.

The Hardy Boys: The Mystery of the Diamond Triangle (1977)

S01E04 - While in the air, Nancy sees a car go off the road, and reports it. Everyone says the road is not been used since the bridge went down. Searching for that special car leads her to a young mechanic, but as they open the barn-doors? IMDb.

The Hardy Boys: The Mystery of Witches' Hollow (1977)

S01E03 - On a trip to a retired police captain's country home, the boys and their friends find him missing and themselves plagued with mysteriously threatening happenings that seem related to an old local legend. IMDb.

The Hardy Boys: The Mystery of Pirate's Cove (1977)

S01E02 - Nancy suspects something is amiss when an abandoned lighthouse mysteriously activates. IMDb.

The Hardy Boys: The Mystery of the Haunted House (1977)

S01E01 - Joe and Frank Hardy, suspicious of their father's "fishing trip," follow him and become involved in the search for an amnesiac ex-soldier being chased by killers for some secret he knows. They end up at a club called the Haunted House that has mazes, trapdoors, and secret passageways. Wikipedia.