'Fire,' Merryl said dully, after they had moved less than a hundred spans.

Tiaan kept going until it was certain there was no way past. 'What now?'

'Resign ourselves to death.'

It was hot here. Tiaan went back to the entrance to the tar tunnel. She could not resign herself to dying. Turning the construct again, she stared at the oozing face of the tar.

'Tell me about the Great Seep, Merryl.'

'It's a good league across, and hundreds of spans deep. Some say it's bottomless. Things, and creatures trapped in it, sink down and sometimes appear again, countless years later, with the wheeling of the slow currents in its depths.'

'If we remain here,' she said absently. 'We'll be dead within the hour.'

'I'd-say so.'

'How long would the air in the construct last with the hatch down, and all of us inside?'

'I don't know. Two hours? Three? Four, possibly.'

'Then let's live those extra hours. Let's risk it.' Tiaan slammed the hatch, took a deep breath and moved the construct gently forwards until it met the convex face of the tar.

Merryl's eyes met hers. Tiaan's eyes were alive for the first time since he'd met her. 'What have we got to lose?'

The construct met resistance and stalled. Tiaan moved the controls, just a tickle. The skinned tar broke and the machine surged into treacly material that smeared across the screen. Everything went black.

'Are we even moving?' whispered Tiaan. 'I can't tell.'

Merryl looked through the rear screen. 'We're going about two spans a minute. The tar's coming over the top. I can't see anything now.'

She nudged the trumpet-shaped lever. There was no sense of motion. 'It's not fast enough. It'll take an hour to get to the end and we've still got to go up to the top of the seep. How far below ground are we?'