getting to watford junction

Part of the answer will depend on where your starting place is. There can be confusion about the relationships and names of the different rail options in and around London. There are 19 independent privatized franchised railways in England, called Train Operating Companies (TOCs), also referred to as National Rail. On the line between Watford Junction and London Euston there are three TOCs. One is Virgin Trains, but they do not serve local customers between London and Watford. Their trains from London are pick-up only at Watford, and their trains to London are set-down only. Southern Railway has an hourly service from East Croydon/Clapham Junction/Kensington Olympia and is a very good choice for people staying in Kensington, South Kensington, and areas around there. London Midland run a frequent service, both fast (15 minutes +-) and slow (18-20 minutes) several times an hour from Euston. Fast trains are non-stop, slow ones stop at Harrow and Wealdstone, and Bushey on the way. A very few services also call at Wembley Central and /or Queens Park. The Underground is operated by Transport for London. So is Dockland Light Railway and London Overground. The London Overground is a slow commuter shuttle which runs between Euston and Watford but it stops at every stop and takes 47 minutes to make the journey. If coming from the Paddington / Marylebone areas you could take the Bakerloo Underground line to Harrow and Wealdstone where you can change onto the London Midland or Overground. All of these accept Pay As You Go Oyster cards and you must tap out at Watford. If you have loaded a Travelcard onto your Oyster instead of Pay As You Go it will not be valid to Watford which is equivalent to beyond Zone 10. You have to have sufficient credit. Or you can buy a ticket; no advantage to advance purchase. Does that help or make it worse?

Well....it is just as complicated as I feared. On the other hand, it's very helpful to know that it's important to know exactly which train to Watford Junction we are getting on. I suppose we can find a staff member to guide us when we get there? Thanks, Nigel!

One other thing. I deduce from your answer that if we have a pay as you go Oyster card, we are good in any zone?

Megan, please say the general area you will starting the journey from. I'll simplify but you need to help. Yes, if (only if) there is sufficient Pay As You Go credit on your Oyster you can go anywhere Oyster is valid. The cost is based on time of day and start and end points.

We are coming from our hotel in the Tower area. We plan to go to the Baker St. tube station, then stop at the Sherlock Holmes museum, before walking to Euston and picking up the train to Watford Junction. Is that a good plan?

I'm running to work so only a quick answer. Its a pretty good walk Baker Street to Euston. Far better to hop the northbound Bakerloo Line Underground from Baker St 16 stops to the end and change to the train at Harrow and Wealdstone...