Help needed with plot line

[Primehunter74]

Alright, I'm working on a campaign. This should be my first one I actually plan on finishing (I have a few interesting yet unfinished ones.) But I dont know if this is a good idea or not. The PC's get hired by an unknown group to clear out a tomb of a famous dwarf hero of raiders, and bring his legendary axe back to their contact (a 2nd lvl gnome rouge were-rat.) Now, after traveling to meet this unknown group, name still undecided, and doing another task for them, they are again to return to this tomb to find out that the heros coffin actually hid the entrance to the REAL tomb of said dwarf hero.

My question is, is this a good idea? Should I do something else? Please give advice if you can.

A few things I did to fix things up and some details:
Since the "tomb" they enter is only the entrance to the real tomb, the axe they get is fake, so they wont be able to use an overpowerful item. Also, the group of raiders or bandits works for a group that the PC's will later have to take down in the future.

[Beowulf DW]

1. Find a reason why this mysterious group needs the PCs to find the axe. Does one of the characters have a special skill that is necessary? Are the other groups resources tied up elsewhere? Think of something.

2. Give the fake axe somekind of special property. Doesn't have to be powerful, just so long as it's above average, or at least interesting. Why should you do this? Because you're more or less implying that the first tomb is meant to throw off grave robbers so that the real tomb will remain safe. That means that you have to make the fake axe valuable enough to convince people that it's the genuine article, that way they won't spend much time snooping around.

[Reynard]

So there's only one important dungeon, and they visit it twice? That might work, although it'll need to be interesting.

Are you going to have a chance of finding the real tomb on their first visit?
What level are they going to be when they get there, roughly? I
f you don't expect them to be much high than 5th You could set a Search DC of 30+ on the secret entrance, so if, for example, the rogue searches the coffin and takes twenty, they aren't annoyed why they come back and find that there was a secret door that you deliberately made invisible for reasons of plot. Of course, this means that there is a chance they'll skip part of your planned storyline.

[Primehunter74]

Beowulf DW:
The group who hired the raiders is named "The cult of the frozen dagger". They give you promises of power and glory and when you get high enough in their ranks your soul is ripped out and replaced with that of a demon from another realm. As the group name implys the demons have to do with ice. The Hero who defeated them (who has a name, but that's unimportant right now) defeated them with him flaming battleaxe. The Cult wanted to obtain the axe and destroy it. Also, the group that hired the PC's knows the tomb is a fake, but wants low level PC's to kill the raiders so that they wont bring the axe back and go "Hey! This is a fake!" and go to look again. If the PC's retreive the axe, the group that hired them can keep it safe and the Cult will think it's in their hands and leave the tomb alone. Also, the fake is a flaming battleaxe, bt the original has a bunch of other cool abilities.

Reynard:
The initial visit is meant to be 1st level, and the second visit I have not yet decided, more than likely 5th level or so. This campaign is meant to take the PC's from 1st to 8th or so. The coffin is magically fised over the entrance, so they wont go "Look a secret switch!" and pull it.

There are still other things I need to work on, it's a work in progress that I will be dedicating alot of time to this summer.