Can't Always Be A Hero

Demi London has managed to survive through 16 years of being a teen spy. However following an incident, Demi is permanently replaced with Ally, one of Zoe's many sisters. Can she ever replace Demi though? Can everyone move on? What happens when a familiar face returns to the team? (Zoe/Dan, Frank/Stella and mentions of Tom/OC) {Has been adopted}