"The secret followed him to the grave."
Translation:Hemmeligheten fulgte ham i graven.
Let me guess (not being a native speaker, and also making this mistake, ending up on this discussion page ;-) )
English: followed to the grave is English idiom, meaning the secret is buried with him (so in fact, it followed him into the grave)
Norwegian: fulgte ham til graven: means more: accompanied him to the grave (to honor him). It might imply that the secret left after the burial to drink a cup of coffee ;-)
While the intended message is that the secret is put in the grave, together with the deceased one. Thus, i graven
And now I hope a native Norwegian speaker pops up and either confirms this, or starts laughing out loud ;-)