Romance might finally be blossoming with Tamla Kari's comely Constance, but elsewhere d'Artagnan's fortunes are less favourable. He's yet to become a true Musketeer and a new nemesis also lurks on the horizon, the fearsome brute Labarge - with guest star Vinnie Jones taking on the sort of period villain role he's not attempted since the music video for Westlife's 'Bop Bop Baby'.
Jones might be a one-trick pony, but it's a trick he's undeniably good at performing and it's enormous fun seeing his cockney hardman routine relocated to 17th Century Paris.
Labarge - a man with "no more humanity than a jackal" - is swiftly recruited by the cunning Cardinal (Peter Capaldi) and serves as his representative in a contest against the Musketeers, with d'Artagnan desperate to face the not-so-gentle giant to repay a personal slight and prove his worth to his friends, the King and the woman he loves.
With plenty of action, intrigue and Vinnie Jones doing what he does best, 'The Challenge' is a fast-paced, colourful romp that also manages to advance the series arc, with d'Artagnan's victory finally securing his position as a bona fide Musketeer. With his promotion coming soon after his first clinch with Constance, it's clear that Adrian Hodges and his writing team aren't afraid of taking big steps forward.
Further fun is offered up this week by Maimie McCoy's magnificent Milady de Winter, who saucily saunters about, toying with all the men around her and delivering lines like "You underestimate my powers of seduction!" with aplomb.
The love square between d'Artagnan, Constance, Milady and Athos (Tom Burke) can only end in disaster - was Athos' staunch support of d'Artagnan this week, not to mention their training scenes, a foreshadowing of a conflict between the two men once Athos learns of his young friend's connection to his former love?
'The Challenge' features one final plot thread, but it's perhaps the one element that Susie Conklin's script could've done without. Not only is Porthos' pursuit of Zoe Tapper's wealthy widow Alice Clerbeaux rather predictable - with his plan to romance and fleece her complicated when her kindly nature warms his heart - but it's not allocated enough screen-time to really register with the viewer.
Porthos being tempted to leave the Musketeers for love could've been its own episode - in fact, 'The Homecoming' did cover similar ground - but here it's swamped by the contest and Milady's manoeuvrings and, as a result, feels undernourished.
'The Challenge' might've been better off if it had excised this element completely and spared more time for further interactions between Milady and Athos or a backstory for the fun but rather one-dimensional LeBarge.
That quibble aside, a winning blend of strong performances, a fast pace and a welcome resurgence for d'Artagnan sees The Musketeers come up trumps again this week. If the one major flaw in 'The Challenge' is attempting to do much in a single episode, then you can't really hold the show's ambition against it.