This final entry in the Rusty series seems to know what the first Rusty film did not - that it is part of a series, and as such it tries to tie up any loose ends appropriately.
First off, this entry gives you a big dose of Rusty as he is sold by a burglar to an unknowing couple passing through town and only manages to get away and head back home after he is a couple of hundred miles from Lawtonville. On the way back he meets up with the Neeley family, two sons and their widower father who is trying to eke out a living doing day labor traveling from town to town. As chance would have it the Neeley family is headed back to Lawtonville, now with Rusty in tow, thinking he is a stray since he has no collar. In the meantime, Danny and his friends are out literally beating the bushes looking for Rusty who is missing, in part, because Danny did not follow the law and his dad's advice and keep Rusty's collar on him along with his registration. When Danny and his friends find Rusty with the Neeleys Danny immediately yells "theif!" not believing their claims that Rusty had been found so far away. Getting the attention of a nearby policeman with his ruckus, Danny causes temporary legal problems for the Neeleys who, due to their unstable financial status and state to state existence, don't have their automobile tags and registration in order.
Things turn around quickly for the Neeleys though as Hugh Mitchell offers Mr. Neeley a chance to sharecrop some land he has. When Danny sees the youngest Neeley being babied by his mother and Rusty seemingly taking up with the boy, at first he decides to go to military school and give Rusty to the youngest Neeley. However he soon learns you can't give away what you think you've already lost and call it generosity - the affection of his mom and of Rusty.
This last entry in the series really comes full circle with the Neeley family being in the same place emotionally that Danny and Hugh Mitchell were in the first film, although they are certainly living a much more financially modest life than the Mitchells were. The youngest boy needs a mother, a home, and a dog to call his own. The oldest son at first resents the woman who takes an interest in his father. Most of all the film makes the point that although Danny is grown, he'll never outgrow some things - like Rusty and the love and interest of his parents.
The last scene is rather strange as the Neeleys and the Mitchells celebrate Rusty's birthday since, if you remember the first film, there would be no way to know that date since Rusty was originally a German war dog. But then heart, not consistency, has been the trademark of this series anyways.
I don't think Sony/Columbia will ever release all of the Rusty films together in a set because there is just too much inconsistency between entries as I have already mentioned. In the first film, Mrs. Mitchell is Danny's stepmom and Lawtonville must be on the coast because German spies land via sub near the town. By the last entry Lawtonville is clearly mentioned as being in Illinois - making a submarine landing impossible - and Danny's stepmom has been transformed into his actual mother.
If you like the other Rusty films I'm sure you'll like this one too.