They stopped in front of one particular tree that grew in two parallel trunks from a peculiar crotch near the ground, as though it had once been struck by lightning. Birk faced the tree and said, “Birk Aaland. Open sesame.”
The whimsical code phrase, matched to a recording of his own voice, triggered the door to open. In a clearing just beyond the split tree, a large grassy section of ground slid back to reveal a steep broad ramp leading downward into the earth. Birk and Arthur strode down the slope, and the cover slid back into place over their heads as soon as they’d passed. The two continued down the ramp until they were ten meters below ground and their progress was stopped by a heavy metal wall in front of them.
If they’d been unwelcome intruders, the city’s defenses could have disp
