An illuminating theme -- light -- ignites the bakers' creativity in the kitchen. Guest judge: actor Irene Choi ("Insatiable").

Married bakers who live and work together say "I do" to delicious sweets. Guest judges: husband-and-wife TV hosts Nick and Vanessa Lachey.

The bakers bring their A-game in a trio of inventive, science-inspired rounds. Guest judge: actor Paris Berelc ("Alexa & Katie").

A family theme stirs fond memories for tight-knit bakers who are brothers and sisters, mothers and sons and more. Guest judge: chef Carla Hall.

The contestants serve up sweets with summery flavors that evoke the great outdoors.

An ocean theme sends bakers into the deep to make seascapes, aquatic creatures and salty-sweet flavors.

Sweet and salty snacks yield yummy flavors over a trio of junk food-inspired rounds. Guest judge: comedian Fortune Feimster.

The teams wax nostalgic with extra-sweet treats inspired by popular candies.

Geeky science-themed challenges get the creative juices flowing -- along with oozy zombie 'blood.'

The baking teams pour buzz-worthy ingredients like coffee, honey and alcohol into amazing edible creations.

The teams work to wow the judges with confections that bring the element of surprise.

Magical cupcakes, edible illusions and levitating cakes? What sorcery is this?! Guest judge: magician Justin Willman ("Magic for Humans").

Teams take a tropical vacation with bold agendas and breezy flavors. Guest judge: actor Garcelle Beauvais (“The Real Housewives of Beverly Hills”).

Fashion-forward challenges force the frazzled contestants to think outside the box.

From lofty nests to baking with insects, these avian-themed challenges are for the birds. Guest judge: actor and singer Naya Rivera ("Glee").

The bakers rush to make winning desserts inspired by the judges' favorite holidays.

A darkly delicious blackout theme puts the bakers to the test — and the results are decadent. Guest judge: actor and musician Tyler Posey ("Teen Wolf").

Breakfast-, lunch- and dinner-themed challenges determine which team is the hungriest for victory. Guest judge: celebrity cake designer Ron Ben-Israel.

Bakers who first met online attempt to re-create popular dessert trends and serve up the next big thing. Guest judge: "Candy Queen" Jackie Sorkin.

As time ticks down on three chocolate-themed rounds, the bakers try not to lose their tempers. Guest judge: chocolatier Jacques Torres ("Nailed It!").