By the Light of the Study Lamp is the first book in The Dana Girls detective series, originally produced by the Stratemeyer Syndicate.

[1]: 2  While the girls are distracted, having gone to the aid of their clumsy maid, Cora "Applecore" Appel, the lamp is stolen from their home, and though the sisters give chase in the family roadster, their search reaches a dead-end at an antique store run by the sinister Jake Garbone.

She informs Louise of this, and they walk past the shop again, observing the same mysterious woman peeking at them from behind the curtains and then disappearing.

[1]: 19, 23 On the way home, the girls encounter a handsome man of about thirty-five who asks them for directions to their uncle's house before being distracted when a passing truck strikes his dog, knocking it into the nearby Oak River.

The river leads to the treacherous Oak Falls, and the quick-acting Jean rescues the dog by leaning out over a rock and extending her hand, while thoughtful Louise first gets a rope from the trunk of their roadster and ties it around her waist so that she can swim out to rescue the young man without being swept away by the current; Jean pulls on the rope to assist while her sister gradually swims both herself and the victim to shore.

Both are surprised by the soaking wet stranger: clumsy "Applecore" drops the tray of cookies she was preparing, while Aunt Harriet sends for the family's hired man, Ben Harrow, and has him carry the stranger to Uncle Ned's unoccupied bedroom, and sends for a physician to attend the young man in a house call.

Uncle Ned, having arrived home from port in New York, where he ended his latest sea voyage, earlier than expected, noticed that there was a party going on, and decided to sneak upstairs to freshen up and change before joining the festivities.

After cleaning up, the captain and Starr join the party, where both they and the guests learn the story of the river rescue from the Dana girls.

They also learn that Franklin's grandfather built the Starhurst estate, which the Starr family had to sell after a number of financial setbacks.

Franklin Starr asks to be dropped off at the train station, saying that he has important business to attend to, and using the excuse of his ongoing headaches making him poor company, which helps to blunt Uncle Ned's objections.

The 1949 edition of the book featured a new cover in the full-color wrap style used on Nancy Drew, the Hardy Boys, and other Grosset and Dunlap series.