Yes you do get your original stake back.
Example
William hill - Dog's - *meeting / race time*
Stake for Dog nu * to win - £5.00
Odds (you can ask for the odds at time of placing bet to ensure fixed odd's) -4/1
If your selected Dog wins, 1st place
Return - £25.00 in Total.
1x original stake (£5.00) = £5.00
Think this is the simplest way I can explain, lol.
4x £5.00 = £20.00 winnings