Tonight on Castle there are more ticks than treats as Rick and Kate investigate a bizarre Da Vinci Code-style murder.

As you recall, last week’s episode was focused on time travel, which Rick noted was his favorite case ever. This week’s episode may make him rethink that statement.

This “Get a Clue” episode also continues Alexis’ story line from last week. She and Pi have officially moved in together, much to the pain of Rick. The ending scene from last week was Alexis packing the last of her items and leaving the apartment. This week’s promo images show Martha and Rick visiting Alexis and Pi at their new apartment. Only time will tell how Alexis moving out will affect Rick, but for now he seems pretty frustrated and upset by her decision.

“Get a Clue” synopsis:

Castle and Beckett investigate the bizarre murder of a young woman who was found ritually posed. When the team finds a collection of strange symbols in her apartment and the prime suspect turns out to be a mysterious monk, Castle becomes convinced they’ve stumbled onto a “Da Vinci Code” style conspiracy. Meanwhile, Castle tries to come to grips with the fact that Alexis and Pi have moved in together.

Castle airs tonight on ABC at 10PM EST.