One thing you must realise is that there is no such thing as pure iron/steel these days. Iron/steel isn't nearly as strong now as it was in medieval times. However, with that said, iron in early medieval times was so soft you could hack right through a helm with a sword and leave a nice lil mark on the skull (depending on the grade of iron used on the sword and the helm, ofcaurse). After many hundreds of years of fine tuning, however, the only use the sword had was to puncture the plate. That was very difficult, however, since the grade of steel was so hard... only blunt instruments and weighted axes had any use against plate armor in later medieval times. Makes me wonder why rapiers were so popular then and why less people wore plate (Other than it's obsene costs... a nice suit of armor would cost as much as a nice lexus does now... and a kings suit would be as much as a rols royce).
A vicious murder happens in a town that the party happens to pop in at. Under heavy suspicion as they are strangers, the party is forced to discover the perpetrator or have their reputations blackened, especially as more and more murders occur in the town, and mysteriously stop and restart when the party leaves to go kill off that evil necromancer who kidnapped the princess.
The only problem is that a demon, possessing one of the party, is the perpetrator. And the demon makes no signs that its living in the PC's head.
In fact, for all the party knows (except for the possessed person's), their companion is an evil murderer.
Do they try and execute their friend as he's a vicious murderer, and no evidence points to demonic posession? Or do they flee town with him, trusting him, and have their reputations destroyed?