Poseidon's Trident is a seafood shack in Malibu, Los Angeles.
Poseidon's Trident is a ramshackle building with a neon sign bearing the name of the restaurant. Behind the restaurant is an outdoor shower and a double sink, while there are picnic tables in front of it. Motorcycles are often parked out front.
In August 2012, after staving off a Mantid demon attack at the ley line convergence, Emma Carstairs, Julian Blackthorn, Cristina Rosales, and Mark Blackthorn stopped by the restaurant—where Emma and Jules have gone to in the past, recalling having eaten fried oysters and tartar sauce at the place—to get a bite to eat and tend to Emma's wounds. Julian, Emma, and Mark showered in the back. With Jules and Emma alone, the former hinted at his feelings for her, and Emma was just about to respond before their companions returned.
The group of Shadowhunters continued their investigation while resting here, using the time to examine Stanley Wells' wallet. When Jules offered to heal Mark's injury with a rune, he refused, telling them that he was still afraid to be marked with runes. Mark took his shirt off and showed them the scars on his back, obtained when faeries of the Unseelie Court cut runes into his skin with knives. Horrified, Julian assured him that he and the rest of the family will care for him.