- Critical Research Failure: In "Plan of Attack," a Catholic man goes to confessional for breaking the Sixth Commandment—committing murder. In Catholicism, this is the Fifth Commandment.
- Fan-Preferred Couple: Despite a 27-year age difference between the characters, 73 percent of Foyles War related fanfics found on Fan Fiction Dot Net as of the beginning of 2012 romantically pair Christopher Foyle and his driver Samantha Stewart.
- Genius Bonus: Or at least a bonus for the musically literate. A piano piece that is heard several times in "Elise", associated with the episode's title character, is not identified beyond a remark that Ludwig van Beethoven is perhaps not a tactful choice given the war; it's Beethoven's Bagatelle No. 25 in A minor, "For Elise".
- Harsher in Hindsight: the death of poor Lucy Smith in Eagle Day. In the episode, it's generally regarded as an innocent young girl seduced by an older man, in over her head, who commits suicide over her resulting pregnancy, which is subsequently covered up because the man concerned is a key part of an experimental program. Which doesn't stop Foyle from telling the man's superior "What he did to Lucy Smith might not have been strictly criminal, perhaps, but it was immoral, improper, and downright disgusting." When re-watched in the wake of the Harvey Weinstein scandal and the #Metoo campaign, it comes across as something far nastier: Major Graham using his position as her superior officer to intimidate and manipulate Lucy into becoming his mistress, partly by implying that providing sexual services to him was part of her job for morale purposes. (On the Wikipedia page, it's stated outright to be sexual assault.) Even worse, as they were both staff members of an experimental scientific program, the whole mess came under the Official Secrets Act, giving Lucy no recourse to the usual chain of command which should have protected her. (whether it would have, given the sexist attitudes of the time, is another discussion altogether) It's no wonder Lucy's father kills Major Graham, and has no regrets whatsoever about doing so.
- Nightmare Fuel:
- The effects of anthrax, in both its deliberate testing on livestock and its accidental spread to humans.
- Also the coffin factory.
- see Harsher in Hindsight above: Besides the sexual assault and subsequent tragedy that kick-starts the mystery, more than one character strongly hint that one of the major hazards of being a servicewoman is fighting off male colleagues who think that the ladies should be providing other kinds of service(read: sexual) as well.
- Retroactive Recognition: The show contains a near-hilarious amount of young British actors who went on to make Hollywood's A-list, particularly James McAvoy (who is best known for portraying the younger Professor Charles Xavier in the X-Men Film Series), Rosamund Pike and Emily Blunt. Also featured are the fresh young faces of David Tennant, Sophia Myles and Tobias Menzies.
- Rewatch Bonus: The identity parade in "Bleak Midwinter." Foyle isn't watching the elderly witness as he walks down the line. He's watching the patrolman who drove him over, after having given the task to that patrolman in the first place.
- Some Anvils Need to Be Dropped: In "A Lesson in Murder", Foyle and Sam investigate a factory where one of the suspects works, which is heavily guarded and under tight government security. It turns out to be a factory run by the Ministry of Health for mass-producing wooden coffins to deal with the expected homefront casualties. You can almost see the anvils falling, but the effect is chilling.
- Uncanny Valley: Laurence Fox's inhumanly creepy performance in "War Games" is very effective. There's just something about the way he moves (or doesn't move) and the wide, unblinking hostility of his stare as he talks to people. It's not surprising that his character turns out to be a Nazi who is unsettling even to other Nazis.
- The Woobie: Susan Gascogine. Her father, a judge, threatens her boyfriend with imprisonment on false charges because he's not posh. She takes in a Blitz evacuee because he seemed unwanted, but her parents hate him for having lower-class manners and she can't connect with him as she'd hoped to. Her father's life is threatened and the young boy dies. When she breaks down in front of Milner, her father walks in and throws him out, and he's soon shot dead. Finally, her own mother confesses to murdering her father, because he had been the one to kill the child.
YMMV / Foyle's War