When a group of wedding guests in Massachusetts suffocate from the inside out, the team must find out how the toxin was delivered and targeted.
Emma, Henry and Mr. Gold search for Gold's son in New York; Hook, Cora and Regina look for one of Rumplestiltskin's most-precious possessions.
After a shift in violent animal behavior, the team tries to rescue Jamie and secure the leopard that may hold the key to curing the animal crisis.