Almost a year has passed since Stella and Tom discovered a time tunnel and travelled to early 1900s London, where they befriended Emma, Lucy and Jack. The magical moles that made the tunnel and secret lake appear have since vanished, but the children are longing to meet again. Then an illness, which puts Emma's life in danger, changes everything. The moles reappear, just when needed, and Lucy realises the only hope of a finding cure lies in the future. So unfolds a thrilling tale of time travel, rekindled friendships and new threats that no one could have foreseen...