Harry whines so much about how he shouldn't have survived that we check the cover to make sure we're not reading Order of the Phoenix.
Coincidentally, he picks up the blanket and reads Albus' message: "Dad. Help. Godric's Hollow. 31/10/81." (4.6.43).
Now the real question is: what were James and Lily Potter doing leaving their baby alone long enough for a stranger to break in and write on his blanket with a magical chemical?