Your favorite mystery novelist is back! “Castle” has been on hiatus since November, but brand new episodes return to ABC on Monday night.

Season 8 will pick up with episode 9, titled “Tone Death.” According to the network’s official synopsis, Castle (Nathan Fillion) and Beckett (Stana Katic) will find themselves wrapped up in another murder – this time involving Castle’s mom, Martha (Susan Sullivan). Martha is fine, but the same can’t be said for one of her fellow performers. The episode description reveals that the husband and wife team will investigate a body found in the theater where Martha performs. The case will lead them into the “unexpectedly dangerous world of competitive a capella.”

Although the Castle and Beckett are working together on a case, that doesn’t exactly mean that things between them are back to normal. As Entertainment Weekly revealed earlier this month, the husband and wife are keeping their rekindled romance a secret. According to the site, Castle has to “come up with a convincing cover to continue working with the 12th precinct.” And as if lying to some of his friends wasn’t bad enough, Castle’s cover will “ruffle a few feathers.”

“They’re back together, but they’re keeping it a secret,” executive producer Alexi Hawley explained to EW. “They’re fighting in public and romancing in private, which adds a little spark to their relationship.”

For those that don’t remember, Beckett and Castle were separated for most of the first half of Season 8 due to Beckett’s decision to investigate the killings from the attorney general’s office on her own. While they joined forces again in the fall finale to solve a murder on a cruise ship, the two were still keeping secrets from each other. Thanks to Hayley’s (Toks Olagundoye) hacking skills, Castle was able to discover that Kate was still working on the Attorney General murders with the help of Vikram (Sunkrish Bala). With everything finally on the table, Kate approached Castle to apologize and ask for his help. Although hesitant at first, Castle ultimately cast his hurt feelings aside and agreed to aid his wife by using their breakup as a cover to take down LokSat.

Watch “Castle” Season 8, episode 9 when it airs on ABC Monday, Feb. 8 at 10 p.m. EST.