The Tome of Wayfaring Souls is a Codex owned by Death in which he documents the tale of Team Sleuth (Possibly, the lives of all other living souls as well.) It was used late in the game as a plot device to serve as a for the adventure so far. This recap is shown here.
The Tome appears to have some form of arcane power, as the mischievous Professor Wasp literally ripped a plot hole through it in an unlockable content episode, causing the storyline to go in disarray as he continued to cause more meddlesome mischief.
Now that he no longer has his Scythe, it will be fairly difficult for Death to update the Tome now that he no longer can write in it.