Just one month before the end of World War I, on October 10, 1918, the mail boat RMS Leinster was sunk by three torpedoes fired by a German U-boat. The ship went down in the cold Irish Sea waters in sight of Dublin and over 500 of the 771 passengers died. Death in the Irish Sea is the fullest exploration yet into this terrible incident. The RMS Leinster was owned and operated by the oldest steamship company in the world, The City of Duplin Steam Packet Company. When the war broke out the boats were drawn into a military role. The four identical mail boats employed on the route were often requisitioned for troop transport, which included rushing troops and munitions from Liverpool to suppress the Easter Rebellion in 1916. The issues of Home Rule and conscription were extremely sensitive and demands for a public inquiry into the sinking of the Leinster were refused. A very limited investigation followed and the findings were censored. Stokes examines in detail a number of significant issues about this infamous sinking. For example, why did German submarine commanders consider these mail boats legitimate targets and have specific orders to sink them; what was the full extent of the military role; why were the repeated pleas to the Admiralty to protect them largely ignored; what caused the second and surprisingly large second explosion; and why was the limited investigation into the affair censored?