[[UsefulNotes/WorldWarII It's January of 1944]]. The British have discovered that the Nazis have developed a new chemical weapon: Sarin, a chemical weapon that, unlike mustard and phosgene gas used in UsefulNotes/WorldWarI before, can't be blocked by a mere gas mask -- it's absorbed through the skin. Knowing that this could seriously derail the allies' plans for the invasion of Normandy, they send in a two-man infiltration team consisting of Mark [=McConnell=], an American M.D. and chemical warfare researcher working for the British at Oxford, and Jonas Stern, a German-born Jew and member of the Palestinian terrorist organization Haganah.
A separate story thread takes place in the Totenhausen concentration camp, where the Nazis' experiments with sarin and other deadly gases are taking place.
The whole novel is framed as a story being told by a Rabbi who had known of Mark [=McConnell=]'s actions to [=McConnell=]'s son, shortly after his funeral and burial.
The novel was written in 1995 by Greg Iles.
!Tropes present in Black Cross:
* BadassIsraeli: The state of Israel didn't exist at this point, but Jonas Stern qualifies.
* BookEnds: The novel begins and ends with a Rabbi friend of [=McConnell=]] telling the story to his son.
* ChekhovsGun: The toggle ropes. Colin Munro didn't make it, but his toggle rope prevented the mission from being a total wash.
* ColorCodedForYourConvenience: Nazi gases were classified by a colored cross on the container: Green cross for suffocating gases (chlorine, phosgene), White cross for irritants tear gas), Yellow cross for blistering agents (mustard gas), Blue cross for gases that blocked molecular respiration (cyanide, carbon monoxide). After the development of tabun, sarin, and soman gases, they had to add a new category: [[TitleDrop black cross]], for nerve agents.
* UsefulNotes/DwightEisenhower: Opposes Churchill's plan to strike at the Nazi gas factories.
* SadisticChoice: Which of Rachel Jansen's children will she save? [[spoiler: Hannah.]]
* [[StupidJetpackHitler Stupid Nerve Gas Hitler]]
* TitleDrop: Both the new category for the new gases, and the name of the mission [=McConnell=] and Stern undertake.
* TrainingFromHell: At Achnacarry Castle.
* TrustPassword: To prove he's Jewish, the inmates at Totenhausen ask Jonas Stern to name the [[https://en.wikipedia.org/wiki/Ma_Nishtana Four Questions]]. Not convinced, one inmate sticks her hand down his pants to see if he's circumcised.
* WellIntentionedExtremist: Jonas Stern initially suggests that the concentration camps be bombed ''while the prisoners are still in them''.