- Caitriona Balfe as Claire Randall Fraser
- Sam Heughan as Jamie Fraser
- John Bell as Young Ian Murray
- Maria Doyle Kennedy as Jocasta Cameron
- Colin McFarlane as Ulysses
- Natalie Simpson as Phaedre
- The episode's title comes from the Latin phrase primum non nocere ("first, to do no harm"). The phrase is strongly associated with the Greek Hippocratic Oath.