CREATE TABLE table_3959 ("Series #" FLOAT, "Season #" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" TEXT, "U.S. viewers  ( million ) " TEXT)

What episode number of the season was written by Tom Garrigus and had 2.31 million u.s. viewers?
SELECT MAX("Season #") FROM table_3959 WHERE "U.S. viewers (million)" = '2.31' AND "Written by" = 'Tom Garrigus'
SELECT MAX("Season #") FROM "table_3959" WHERE "U.S. viewers (million)" = '2.31' AND "Written by" = 'Tom Garrigus'