Jack and Ianto were out Weevil hunting, for actual Weevils for once. Truthfully, it was more of a patrol; during the breeding season, the males could get very territorial and it was safer for everybody if trouble could be prevented. That mostly involved herding wandering Weevils back to the sewers, and tranquillising them when necessary.
The alley was dark and there were suspicious sounds of scuffling, so they advanced cautiously, Weevil spray and guns at the ready.
They didn’t find Weevils, but the way the courting couple took off, looked like they’d avoid alleys in future.
Jack couldn’t stop laughing.