First appearance of Captain Janeway's "Ancient English Holonovel," which seems to be a mash-up of Charlotte Brontë's Jane Eyre and Henry James' Turn of the Screw. The latter was also the basis for a previous Star Trek production Sub Rosa (1994). The Holonovel returns in Learning Curve (1995) and Persistence of Vision (1995).
The title refers to the process of investment of mental or emotional energy in a person, object, or idea when applied to mental processes or psychodynamics.
First of two appearances of Carolyn Seymour as Mrs. Templeton. She had previously appeared on Star Trek: The Next Generation (1987) as Sub-Commander Taris in Contagion (1989), Mirasta Yale in First Contact (1991), and Commander Toreth in Face of the Enemy (1993).
According to Michael Piller, the story was originally inspired by or, at least, had similarities with the Agatha Christie novel And Then There Were None, aka Ten Little Indians.
Tuvok's rank switches from lieutenant commander to lieutenant and back again a number of times. By the end, he is wearing the rank of lieutenant. His rank remains that of lieutenant until Revulsion (1997), in which he is officially promoted to the rank of lieutenant commander. There is no scripted reason why Tuvok's rank changes abruptly, and it may be that it was simply an error in costuming for him to have been wearing a lieutenant commander rank for the first half of the first season; he is addressed as "lieutenant" several times in the first season, despite wearing lieutenant commander rank insignia.