The case of the episode "The Cook" was disappointing and so easily solved. Pentagrams, seduction and an ex-priest, all neatly wrapped. Then everything went up in flames.

Red, though he prefers Tolstoy to Star Wars, once again showed how well he has mastered the Jedi mind trick.
He won a prize: a new member for his team, the arsonist Earl Fagen.

Fagen: "Look, if this is about that fire at Fritzles, I had no idea you were..."

Is Fagen involved in that tragic house fire which Liz vaguely remembers from her childhood?

The second storyline, Liz' quest for Tom's killer, was more interesting, and now we know the truth: the truth is out there.
Everyone, Tom, the bad guys, Red (and Dembe?), except for Liz of course (and the FBI), knows.
But she will find out, and Red can only delay, but not prevent that from happening.
So what is he hoping for by not telling her?

Red: "I have a secret and I need to keep it, even from you."

At the end of the episode, Red and Liz are watching Agnes play at the daycare center.

Red: "I know how hard this is."

Liz: "I need your help to find Tom's killer. I need it, but I don't know if I can trust it."

Red: " You won't miss a day more with her than is absolutely necessary. You have my word."

Liz: "And you have mine. That I'm going to honor Tom's dying wish."

Red: "Which was?"

Liz: "For me to know your truth. Before this is over, I'm going to find out what it is."