"Pheromones," muttered Ianto to himself for not the first time as he mopped up behind the Tourist Office counter. "How did none of us think of that?" Gwen and Tosh's reappearance had snapped Jack from his daze enough to answer a couple of questions as Ianto helped him gather up the jar to take the hand back downstairs.

Given what had happened when Gwen had gone down to the cells on her own, they really should have suspected something. He shook his head, wondering at their apparent attack of collective dimness.

Storing the mop back in the cupboard and flipping the sign on the front door to 'Closed', he made his way back down to the main Hub, intent on offering his assistance to whatever research was sure to be going on to find Carys. He was just in time to witness what he thought had originally been some sort of rodent become nothing more than a splat inside a plastic box.

His suspicions were confirmed a moment later when Owen threw his hands in the air. "Rat jam!"

Ianto stepped up closer to the other, slightly confused as to the purposes of whatever this little experiment had been.

"So, that's what will happen to Carys?" Jack asked, sounding more worried than he had since the case had begun.

Owen didn't answer, a tilt of his head more than enough confirmation for all of them.

"She said she was losing," Gwen said in a small voice. "Down in the cells, that's what she said."

"We need to find her before she loses that battle and takes a leaf from the rat's book," Jack said, shaking his head.

"But where would she go?" Owen asked, coming up from the medical bay where the box containing the former rat still sat.

"Well, the alien inside her wants sex, right?" Ianto asked, looking around the others for confirmation.

"Yeah," Jack nodded. "It feeds on the energy from the orgasm."

"So where is it going to want to go?"

Jack folded his arms and seemed thoughtful for a second. "Lap dancing clubs, brothels… anywhere where there are lots of eager and desperate men, I guess."

Tosh shook her head and sighed at them. Ianto, who thought Jack's suggestions seemed perfectly logical, looked quizzically at her.

"You're thinking like men," she said patiently. "Carys may be possessed by this… sex gas, but she's still a woman." She tilted her head at Gwen. "I don't know about you, but if I was in her situation, I think I know where I'd go."

For a brief flash, Gwen seemed as confused as Ianto felt, and then a light bulb went on behind her eyes and she nodded grimly. "The Ex."

Jack looked at Gwen. "Did you pick up any names for those in all of your profiling? I'm hoping it's a short list."

Turning swiftly, Gwen scurried off, returning less than a minute later with a piece of paper in her hand. "From what I found, there's only one really serious one. This guy." She proffered the page.

"Right," Jack said, reading the page and clapping his hands together. "Ianto, keep an ear out for any odd reports, we have somewhere to be."

Ianto nodded as the four of them ran from the Hub, barely taking a moment to grab weapons and basic toolkits from desks.

***

Struggling to keep his eyes open as he approached thirty-six hours without sleep, Ianto brewed a pot of extra strong coffee while he kept an ear out for any unusual reports coming in that would indicate that Tosh and Gwen's intuition had led them astray.

Ten minutes later, that notion was dispelled as Jack's dispirited voice came over his comms. "Right place, just too late."

"Nothing here, sorry," Ianto replied, quickly flicking through the monitors and feeds once more, just to be sure. "I don't have any clues to give as to where she might be."

"That's okay, Ianto. We'll have a think about it and be back soon if we can't come up with anywhere."

The comm. went silent again, leaving Ianto with just the sounds from the police feeds, the water tower's drips and Myfanwy snuffling in her nest somewhere far above him to keep him company.

***

He startled guiltily out of a light doze when the siren above the cog door went off some time later, the rest of the team clattering through noisily.

"Everyone go home!" Jack was calling before they were even properly into the Hub. "It's been more than a long day and, even though we saved the day this time, who knows what's around the corner!"

"It's been a very long two days, Jack," Ianto said blearily as he made his way across to the others.

"Exactly," Jack said, gesturing around him for them all to hurry up and get sorted out and leave again. He caught Ianto's arm as he was about to go back to collect his jacket. "When Gwen gets in tomorrow…" he started, a cajoling note in his voice.

Ianto raised an eyebrow in question. "Yes?"

Jack tilted his head, clearly trying to appear at his most endearing. "Do Gwen's induction paperwork with her for me? Please?"

Ianto sighed, nodding as he pulled his arm free and snagged his jacket to leave. "Only because you asked nicely," he murmured, realising with some dismay that he wasn't sure if that was actually quite true.