What are you reading now?

[RJNorton]

On p. 57 of Roscoe's The Web of Conspiracy it says, "Druggist Thompson considered Herold reliable enough to be trusted with an errand to the White House. Herold met President Lincoln. He delivered a bottle of castor oil, and Lincoln - probably with some appropriate, thigh-slapping joke - asked to have it charged. On a day for afterthought, David Herold would recall the President's sense of humor."

This (allegedly?) happened when Herold was working as a clerk in Thompson's drug store at 15th and New York Avenue.

There is no footnote for the story.

Truth or fiction?