CW aired the eighth episode of 'Arrow' Season 3 which incorporated a crossover with another CW superhero series 'The Flash' on December 3. Episode 8 entitled "The Brave and the Bold," showcased Oliver Queen and Barry Allen in their attempt to stop a boomerang wielding assassin.

The episode begins with Arrow, Arsenal, and Diggle approaching a house from different sides and confirming their positions, ready to breach it. The three narrowed down the location of the boomerang killer to that house.

However, Arrow notices that the house was rigged with a bomb so he and Arsenal detonated it with their arrows. After the explosion, they searched the house while a group of ARGUS men arrive, telling Arrow to "let it go."

Back at the headquarters, Felicity starts investigating ARGUS, while Oliver sends Diggle to Lyla to make his own investigation about the boomerang killer.

Meanwhile, Cisco and Caitlin suddenly arrive at Sterling City with the intention of getting the DNA from Sara's murder.

Slightly annoyed, Oliver brings Cisco and Caitlin to the "Arrow Cave" for the DNA sample.

Once in the Arrow cave, Cisco freaks when he saw Arrow's "Toys," while Caitlin shows interest in the salmon ladder.

Diggle on the other hand asks Lyla questions about the boomerang killer, which she continues to deflect. After that, they head to ARGUS with the boomerang killer following closely behind.

Arrow and Arsenal go to ARGUS to help, in response to Diggle's call. Not long after, Flash arrives to save the day, but not before boomerang manages to escape.

Back at the Foundry, Barry convinces Oliver to let him help catch the boomerang killer; Ollie agrees but with the condition that it will be done his way. While Cisco and Caitlin are investigating a boomerang they find on the scene, they noticed Kaus Marcos' signature on it.

Flash and Arrow manage to find Marcos, as he hands over an encrypted phone.

Felicity and Cisco use their knowledge of technology to track the signal coming from data on the phone. Following the signal, it leads them to Harkness, which turns out to be a trap as a bomb explodes shortly after they get there.

Harkness used the phone to track Arrow's HQ where he attacked the girls, as Lyla tried to defend Caitlin and Felicity but she was hit by a boomerang. The boys arrive and Flash runs Lyla to the hospital.

Afterwards, Arrow and Flash were able to track down Harkness and imprisoned him on Lian Yu.

Before Barry's team went back to Central city, they exchanged gifts with Ollie's team. Cisco gave Oliver an upgraded costume, and Oliver asked Felicity to install another impractical costume holding glass case for the next time Barry is in town.