The Beast Within is the eighteenth episode of the third season of Shadowhunters: The Mortal Instruments.


A demon outbreak in New York City on Halloween becomes a top priority at the Institute, but as the Shadowhunters hunt the demons, Jace becomes more worried about Clary. Meanwhile, Alec has to juggle the outbreak with his deep concern about Magnus' depression.




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TMI 3x18 Promo Preview

Asmodeus gives Alec an ultimatum to save Magnus, and Clary struggles with her link to Jonathan.


See more promotional images here and stills here


A list of the songs and score music featured in this episode:

  • "Nevermind" - Dennis Lloyd
  • "Digital Heartbeat" - The Silverman Brothers
  • "Light on U" - Alice Gray
  • "Other Matter" - Yon Ort
  • "Necessaries" - Many Voices Speak
  • "Fear of the Water" - SYML


  • This episode was written as a Halloween episode.[1][2][3] It was set to air in October 2018 as part of Freeform's "31 Nights of Halloween" programming,[4][5] before 3B was pushed back to 2019.
  • Filming ran from March 29 to April 14, 2018,[6][3][7][8] with supposedly only eight work days in total during that time.[7]


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