Little errors that she'd made, adding up. A tendency to favor one leg over the other. It had been an iffy thing from the beginning, trying to navigate by dead reckoning.

Finally, though, it was obvious. Here she was. On the shores of Lake Styx. Not all that far off course after all. Three miles, maybe, tops.

Despair filled her.

They'd named the lake during their first loop through the Galilean system, what the engineers had called the "mapping run." It was one of the largest features they'd seen that wasn't already on the maps from satellite probes or Earth-based reconnaissance. Hols had thought it might be a new phenomenon–a lake that had achieved its current size within the past ten years or so. Burton had thought it would be fun to check it out. And Martha hadn't cared, so long as she wasn't left behind. So they'd added the lake to their itinerary.

She had been so transparently eager to be in on the first landing, so afraid that she'd be left behind, that when she suggested they match fingers, odd man out, for who stayed, both Burton and Hols had laughed. "I'll play mother," Hols had said magnanimously, "for the first landing. Burton for Ganymede and then you for Europa. Fair enough?" And ruffled her hair.

She'd been so relieved, and so grateful, and so humiliated too. It was ironic. Now it looked like Hols–who would never have gotten so far off course as to go down the wrong side of the Styx–wasn't going to get to touch rock at all. Not this expedition.

"Stupid, stupid, stupid," Martha muttered, though she didn't know if she were condemning Hols or Burton or herself. Lake Styx was horseshoe-shaped and twelve miles long. And she was standing right at the inner toe of the horseshoe.

There was no way she could retrace her steps back around the lake and still get to the lander before her air ran out. The lake was dense enough that she could almost swim across it, if it weren't for the viscosity of the sulfur, which would coat her heat radiators and burn out her suit in no time flat. And the heat of the liquid. And whatever internal flows and undertows it might have. As it was, the experience would be like drowning in molasses. Slow and sticky.